Sequence Analysis oftheMajorOuterMembraneProtein Genefrom Chlamydia trachomatis Serovar L2

Themajor outer membrane protein (MOMP)ofChlamydia trachomatis constitutes over60%ofthetotal protein ofthe cell wall(5), andinrecent years, investigations haveevaluatedtheantigenic, structural, andfunctional properties of MOMP.Studies ofthespecificities ofbothpolyvalent (7)and monoclonal (26) antibodies toMOMP define anantigenically complex protein thatdisplays type-, subspecies-, andspecies-specific determinants. Theimportance ofMOMP as surface antigen isunderscored byitsroleastheimmunodominant serotyping antigen (7,28,29). Furthermore, neutralization ofchlamydial infectivity through theuseof monospecific (6)andcertain monoclonal (9,14)antibodies specific forMOMP isdemonstrable invitro. Thegrowth cycle ofchlamydiae isrepresented bytwo alternating formsoftheorganism. Theelementary bodyis theextracellular form, whichhasarigid outer membrane, whereas theintracellular reticulate body(RB)hasafragile andplastic outermembrane. Although chlamydiae apparently lackapeptidoglycan (2), thestructural rigidity ofthe outermembraneofelementary bodies ismaintained by disulfide cross-linking ofMOMP andother proteins inhighmolecular-weight oligomers (10, 19). TheRB membrane is notextensively cross-linked, whichisconsistent withits fragile nature (10). Recently, Bavoil andco-workers (3) presented evidence thatMOMP formsporeswhichpermit diffusion ofsolutes through theRBmembrane. Unlike other porin molecules that havebeendescribed, theMOMP poreforming capabilities areactivated ordramatically enhanced whendisulfide bondsarereduced. Thus,thedevelopmental control ofporin function andthestructural changes ofouter membranestability arebothmediated bydisulfide bond interactions. TheMOMP ofC.trachomatis isremarkable forthe multifunctional characteristics thatareknowntodate: it displays molecular weight polymorphism (18), itisacomplexantigen withdemonstrated propensities fordiversity (26), itparticipates inthedifferential structural integrity of thecell wallduring thedevelopmental cycle (10), itforms