Identification of Semaphorin 5A Interacting Protein by Applying Apriori Knowledge and Peptide Complementarity Related to Protein Evolution and Structure

Inthepost-genomicera,variouscomputationalmethodsthatpredictprotein-proteininteractionsatthegenomelevelareavailable;however,eachmethodhasitsownadvantagesanddisadvantages,resultinginfalsepredictions.Herewedevel-opedauniqueintegratedapproachtoidentifyinteractingpartner(s)ofSemaphorin5A(SEMA5A),beginningwithsevenproteinssharingsimilarligandinteractingresiduesasputativebindingpartners.ThemethodsincludeDwyerandRoot-Bernstein/Dillontheoriesofproteinevolution,hydropathiccomplementarityofproteinstructure,patternofproteinfunctionsamongmolecules,informationondomain-domaininteractions,co-expressionofgenesandproteinevolution.AmongthesetofsevenproteinsselectedasputativeSEMA5Ainteractingpartners,wefoundthefunctionsofPlexinB3andNeuropilin-2tobeassociatedwithSEMA5A.WemodeledthesemaphorindomainstructureofPlexinB3andfoundthatitsharessimilaritywithSEMA5A.Moreover,avirtualexpressiondatabasesearchandRT-PCRanalysisshowedco-expressionofSEMA5AandPlexinB3andtheseproteinswerefoundtohaveco-evolved.Inaddition,weconfirmedtheinterac-tionofSEMA5AwithPlexinB3inco-immunoprecipitationstudies.Overall,thesestudiesdemonstratethatanintegratedmethodofpredictioncanbeusedatthegenomelevelfordiscoveringmanyunknownproteinbindingpartnerswithknownligandbindingdomains.