GmapA, a Novel Membrane-associated Protein Influencing Maturation/secretion of Gingipains

Method: Wild-type P. gingivalis W83 and isogenic deficient mutant ΔGmapA were compared with regard to the phenotype and growth rate in vitro. Cell fractionations along with Western blots were used to assess sub-cellular location of maturing gingipains. Further, RNA from mid-exponential growth cells was extracted and analysed for expression of genes involved in PorSS and gingipains. 

Result: ΔGmapA mutant was non-pigmented on blood agar in contrast to the wild-type and its growth was slower in liquid medium with 16 hr retardation as compared to wild-type. Gingipain Arg-specific and Lys-specific activities were dramatically reduced in the ΔGmapA mutant. In contrast to the wild-type in which mature gingipains were associated with the outer membrane, gingipains in ΔGmapA were partially processed and were retained in the periplasm or in association with the inner membrane. However, there was no significant difference on the expression of porT, sov, pg23, pg266, pg543and rgpB between wild-type and ΔGmapA.

Conclusion: GmapA is a novel membrane protein involved in gingipain maturation and secretion. Since the expression level of gingipains and genes related to PorSS remained similar, there seems to be no negative feedback from accumulating partially processed gingipains to regulate PorSS and gingipain expression in the ΔGmapA mutant.