ABSTRACT
Earlymembranebiochemistsdividedmembraneproteinsintotwoclasses:integraland peripheral.Integralmembraneproteinsaregenerallyamphipathicandhaveoneormore hydrophobicpeptidesegmentsofabout23aminoacidsthatspanthelipidbilayer.Peripheral membraneproteins,ontheotherhand,areassociatedwiththemembranebutarecompletely externaltothelipidbilayer.Prototypicperipheralmembraneproteinsarecytoskeletalproteins, suchasspectrinandactin;suchproteinsremainattachedtotheplasmamembranewhenred bloodcellsarelysedowingtointeractionswithintegralmembraneproteinsratherthanwith thelipidbilayeritself.However,morerecently,investigatorshaverealizedthatanumberof proteinscanbeattachedtothemembraneviafattyacidsthatarelinkedtotheproteinandalso insertintothemembranelipidbilayer.Fattyacidssuchaspalmitateormyristatemaybelinked tooneormorecysteineresiduesand,byinsertingintothelipidbilayer,linkthepolypeptide tothemembrane.Asecondmodeofattachmentinvolvesacomplexphosphatidylinositol-glycan (GPI)anchorattachedtotheCterminusofaprotein(Fig.1).Anumberofcellsurfaceproteins areattachedbythislattermeans,whereasseveralcytoskeletalproteinsandcytoplasmicenzymes areattachedtothemembranebycysteine-linkedfattyacids.
