CommonCleavage Pattern ofPolysialic AcidbyBacteriophage Endosialidases ofDifferent Properties andOrigins

Thecleavage specificities ofseven bacteriophage endosialidases degrading thect2-8-linked polysialic acid common tobacterial polysaccharides andtothecelladhesion molecule N-CAM were investigated. The bacteriophages studied represented five different phenotypic groupsbyprotein andDNA fragment analysis and twodifferent morphology groupsbyelectron microscopy. Characterization ofthefragments arising fromthe native or chemically modified substrates ofdifferent sizes showedthatcleavage specificity was influenced by enzyme concentration. Attheinitial phaseofdegradation, atconcentrations ranging from20-to100-fold, the minimum substrate size was an oligomer ofeight (in one case,nine) sialic acidunits that was preferably cleaved atthesame position. Underexhaustive conditions, theoligomers were degraded further, andeachenzyme type hadits own specificity. Thesimilar initial cleavage ofpolysialic acidbyendosialidases associated withphages ofdifferent properties andmorphology suggests a conserved mechanism ofenzyme-substrate interaction. This mechanism may beconformationally determined andrelated tothespecific properties ofpolysialic acidinother molecular interactions. Polysialic acid,a polymerofa2-8-linked N-acetyl