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  <xs:element id="prta_LicenseAgreementTable" abstract="true" name="LicenseAgreementTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <xs:element id="prta_RoyaltyBearingLicenseMember" abstract="true" name="RoyaltyBearingLicenseMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_INDandDevelopmentServicesMember" abstract="true" name="INDandDevelopmentServicesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_SupplyServicesMember" abstract="true" name="SupplyServicesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_ClinicalProductSupplyMember" abstract="true" name="ClinicalProductSupplyMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_CollaborationProgramUSRightsMember" abstract="true" name="CollaborationProgramUSRightsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_RocheMember" abstract="true" name="RocheMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_ResearchReimbursementMember" abstract="true" name="ResearchReimbursementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_LicenseAgreementLineItems" abstract="true" name="LicenseAgreementLineItems" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="prta_CollaborationRevenueLicenseUpfrontPayment" abstract="false" name="CollaborationRevenueLicenseUpfrontPayment" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_MilestonePaymentReceivedClinicalMilestone" abstract="false" name="MilestonePaymentReceivedClinicalMilestone" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_MilestoneAchievementClinicalMilestone" abstract="false" name="MilestoneAchievementClinicalMilestone" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_LicenseAgreementPotentialPaymentUponAchievementofDevelopmentRegulatoryandVariousFirstCommercialSalesMilestones" abstract="false" name="LicenseAgreementPotentialPaymentUponAchievementofDevelopmentRegulatoryandVariousFirstCommercialSalesMilestones" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_LicenseAgreementPotentialPaymentForUSCommercialSalesMilestones" abstract="false" name="LicenseAgreementPotentialPaymentForUSCommercialSalesMilestones" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_LicenseAgreementPotentialPaymentforAchievementofnonU.S.CommercialSalesMilestones" abstract="false" name="LicenseAgreementPotentialPaymentforAchievementofnonU.S.CommercialSalesMilestones" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_LicensingAgreementCostAllocationPercentage" abstract="false" name="LicensingAgreementCostAllocationPercentage" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="prta_LicensingAgreementPortionofRevenueandExpensesAttributabletoCompanyPercentage" abstract="false" name="LicensingAgreementPortionofRevenueandExpensesAttributabletoCompanyPercentage" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="prta_AllocatedConsiderationtoPerformanceObligations" abstract="false" name="AllocatedConsiderationtoPerformanceObligations" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_LicenseAgreementDevelopmentServicesPaymentTerm" abstract="false" name="LicenseAgreementDevelopmentServicesPaymentTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="prta_ResearchAndDevelopmentPaymentToCollaborationPartnerRecordedAsResearchAndDevelopmentExpense" abstract="false" name="ResearchAndDevelopmentPaymentToCollaborationPartnerRecordedAsResearchAndDevelopmentExpense" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_LicenseAgreementMilestonePaymentsPaymentTerm" abstract="false" name="LicenseAgreementMilestonePaymentsPaymentTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="prta_InitialTransactionPrice" abstract="false" name="InitialTransactionPrice" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_LicenseAgreementPotentialAlternativeCommercialSalesMilestones" abstract="false" name="LicenseAgreementPotentialAlternativeCommercialSalesMilestones" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_CollaborationProgramUSTauBMS986446FkaPRX005Member" abstract="true" name="CollaborationProgramUSTauBMS986446FkaPRX005Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_CelgeneMember" abstract="true" name="CelgeneMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_CollaborationProgramGlobalRightsMember" abstract="true" name="CollaborationProgramGlobalRightsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_BristolMyersSquibbMember" abstract="true" name="BristolMyersSquibbMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_BMSFormerlyCelgeneMember" abstract="true" name="BMSFormerlyCelgeneMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_USRightsAndGlobalRightsMember" abstract="true" name="USRightsAndGlobalRightsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_CollaborationRevenueUSLicenseMember" abstract="true" name="CollaborationRevenueUSLicenseMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_CollaborationRevenueUSDevelopmentServicesMember" abstract="true" name="CollaborationRevenueUSDevelopmentServicesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_CollaborationProgramUSTauBMS986446Member" abstract="true" name="CollaborationProgramUSTauBMS986446Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_CollaborationProgramGlobalTauBMS986446Member" abstract="true" name="CollaborationProgramGlobalTauBMS986446Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_CollaborationRevenueSupplyAgreementMember" abstract="true" name="CollaborationRevenueSupplyAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_CollaborationProgramUSThirdProgramMember" abstract="true" name="CollaborationProgramUSThirdProgramMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_CollaborationProgramGlobalThirdProgramMember" abstract="true" name="CollaborationProgramGlobalThirdProgramMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_CollaborationProgramGlobalAndUSThirdProgramMember" abstract="true" name="CollaborationProgramGlobalAndUSThirdProgramMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_CollaborationProgramGlobalPRX019Member" abstract="true" name="CollaborationProgramGlobalPRX019Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_CollaborationAgreementUpfrontPayment" abstract="false" name="CollaborationAgreementUpfrontPayment" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_CollaborationAgreementPotentialRegulatoryandCommercialMilestonePaymentsPerProgram" abstract="false" name="CollaborationAgreementPotentialRegulatoryandCommercialMilestonePaymentsPerProgram" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_CollaborationAgreementExtensionFeeperExtensionPeriod" abstract="false" name="CollaborationAgreementExtensionFeeperExtensionPeriod" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_SaleofStockPremiumReceivedonTransaction" abstract="false" name="SaleofStockPremiumReceivedonTransaction" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_CollaborationAgreementExpectedAllocationofInitialTransactionPrice" abstract="false" name="CollaborationAgreementExpectedAllocationofInitialTransactionPrice" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_CollaborationAgreementTotalTransactionPricePRX019US" abstract="false" name="CollaborationAgreementTotalTransactionPricePRX019US" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_CollaborationAgreementUpfrontPaymentPaymentTerm" abstract="false" name="CollaborationAgreementUpfrontPaymentPaymentTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="prta_CollaborationAgreementPotentialRegulatoryMilestonePaymentsPerProgram" abstract="false" name="CollaborationAgreementPotentialRegulatoryMilestonePaymentsPerProgram" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_CollaborationAgreementPotentialCommercialMilestonePaymentsPerProgram" abstract="false" name="CollaborationAgreementPotentialCommercialMilestonePaymentsPerProgram" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_CollaborationAgreementOptionFeesandMilestonePaymentsPaymentTerm" abstract="false" name="CollaborationAgreementOptionFeesandMilestonePaymentsPaymentTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="prta_CollaborationProgramDiscountRate" abstract="false" name="CollaborationProgramDiscountRate" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="prta_CollaborationAgreementAllocationOfInitialTransactionPrice" abstract="false" name="CollaborationAgreementAllocationOfInitialTransactionPrice" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_DeferredRevenueNoncurrentReclassifiedToDeferredRevenueCurrentAmount" abstract="false" name="DeferredRevenueNoncurrentReclassifiedToDeferredRevenueCurrentAmount" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_CollaborationAgreementTotalTransactionPricePRX005US" abstract="false" name="CollaborationAgreementTotalTransactionPricePRX005US" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_CollaborationProgramUSLicenseAgreementUpfrontPayment" abstract="false" name="CollaborationProgramUSLicenseAgreementUpfrontPayment" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_RevenueFromLicenseAndIntellectualPropertySharePurchaseAgreement" abstract="false" name="RevenueFromLicenseAndIntellectualPropertySharePurchaseAgreement" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_CollaborationProgramOptionExerciseFee" abstract="false" name="CollaborationProgramOptionExerciseFee" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_CollaborationAgreementExerciseFeeUSRightsPerProgram" abstract="false" name="CollaborationAgreementExerciseFeeUSRightsPerProgram" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_CollaborationAgreementTotalTransactionPriceTauBMS986446Global" abstract="false" name="CollaborationAgreementTotalTransactionPriceTauBMS986446Global" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_CollaborationRevenueTransactionPrice" abstract="false" name="CollaborationRevenueTransactionPrice" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_CollaborationAgreementPotentialDevelopmentAndRegulatoryMilestonePayments" abstract="false" name="CollaborationAgreementPotentialDevelopmentAndRegulatoryMilestonePayments" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_CollaborationProgramUSPRX019Member" abstract="true" name="CollaborationProgramUSPRX019Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_CollaborationRevenueDevelopmentServicesForPhase1ClinicalTrialMember" abstract="true" name="CollaborationRevenueDevelopmentServicesForPhase1ClinicalTrialMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_SharePurchaseTransactionAbstractAbstract" abstract="true" name="SharePurchaseTransactionAbstractAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="prta_SharePurchaseAgreementTable" abstract="true" name="SharePurchaseAgreementTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <xs:element id="prta_NovoNordiskMember" abstract="true" name="NovoNordiskMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_TransitionServices" abstract="false" name="TransitionServices" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_SharePurchaseAgreementUpfrontPayment" abstract="false" name="SharePurchaseAgreementUpfrontPayment" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_SharePurchaseAgreementPotentialPaymentUponAchievementOfDevelopmentAndSalesMilestones" abstract="false" name="SharePurchaseAgreementPotentialPaymentUponAchievementOfDevelopmentAndSalesMilestones" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_NearTermClinicalMilestone" abstract="false" name="NearTermClinicalMilestone" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_NumberofVotes" abstract="false" name="NumberofVotes" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="prta_UNDERWRITTENPUBLICOFFERINGTable" abstract="true" name="UNDERWRITTENPUBLICOFFERINGTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <xs:element id="prta_UnderwrittenPublicOfferingMaximumNumberOfSharesUnderwritersOptionToPurchase" abstract="false" name="UnderwrittenPublicOfferingMaximumNumberOfSharesUnderwritersOptionToPurchase" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="prta_December2021AtTheMarketOfferingMember" abstract="true" name="December2021AtTheMarketOfferingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_February2024ProspectusAtTheMarketOfferingMember" abstract="true" name="February2024ProspectusAtTheMarketOfferingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_SaleOfStockMaximumAggregateOfferingPriceValue" abstract="false" name="SaleOfStockMaximumAggregateOfferingPriceValue" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_CommonStockCumulativeNumberOfSharesIssued" abstract="false" name="CommonStockCumulativeNumberOfSharesIssued" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="prta_ProceedsFromIssuanceOfCommonStockCumulativeGrossAmount" abstract="false" name="ProceedsFromIssuanceOfCommonStockCumulativeGrossAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_StockIssuanceCostsCumulativeAmount" abstract="false" name="StockIssuanceCostsCumulativeAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_ProceedsFromIssuanceOfCommonStockGross" abstract="false" name="ProceedsFromIssuanceOfCommonStockGross" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_ShareRepurchasePlanMember" abstract="true" name="ShareRepurchasePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_ShareRepurchaseProgramUnpaidCost" abstract="false" name="ShareRepurchaseProgramUnpaidCost" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_AmendedAndRestated2018LongTermIncentivePlanMember" abstract="true" name="AmendedAndRestated2018LongTermIncentivePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_A2012LongTermIncentivePlanMember" abstract="true" name="A2012LongTermIncentivePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_A2020EmploymentInducementIncentivePlanMember" abstract="true" name="A2020EmploymentInducementIncentivePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="prta_ShareBasedPaymentArrangementEstimatedForfeitureRate" abstract="false" name="ShareBasedPaymentArrangementEstimatedForfeitureRate" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="prta_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValueRelatedToVestedOptions" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValueRelatedToVestedOptions" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedAndExpectedToVestNumber" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedAndExpectedToVestNumber" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="prta_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedAndExpectedToVestWeightedAverageGrantDateFairValue" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedAndExpectedToVestWeightedAverageGrantDateFairValue" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="prta_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedAndExpectedToVestWeightedAverageRemainingContractualTerms" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedAndExpectedToVestWeightedAverageRemainingContractualTerms" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="prta_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueNonvestedAndExpectedToVest" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueNonvestedAndExpectedToVest" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_IncomeTaxesTable" abstract="true" name="IncomeTaxesTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <xs:element id="prta_IncomeTaxesLineItems" abstract="true" name="IncomeTaxesLineItems" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="prta_DeferredTaxAssetsPeriodIncreaseDecrease" abstract="false" name="DeferredTaxAssetsPeriodIncreaseDecrease" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="prta_RestructuringReserveSettledWithoutCashPeriodIncreaseDecrease" abstract="false" name="RestructuringReserveSettledWithoutCashPeriodIncreaseDecrease" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
</xs:schema>
