The liposoluble proteome of Mycoplasma agalactiae: an insight into the minimal protein complement of a bacterial membrane

The selective enrichment for M. agalactiae PG2T liposoluble proteins was accomplished by means of Triton X-114 fractionation. Liposoluble proteins were subjected to 2-D PAGE-MS, leading to the identification of 40 unique proteins and to the generation of a reference 2D map of the M. agalactiae liposoluble proteome. Liposoluble proteins from the type strain PG2 and two field isolates were then compared by means of 2D DIGE, revealing reproducible differences in protein expression among isolates. An in-depth analysis was then performed by GeLC-MS/MS in order to achieve a higher coverage of the liposoluble proteome. Using this approach, a total of 194 unique proteins were identified, corresponding to 26% of all M. agalactiae PG2T genes. A gene ontology analysis and classification for localization and function was also carried out on all protein identifications. Interestingly, the 11.5% of expressed membrane proteins derived from putative horizontal gene transfer events.This study led to the in-depth systematic characterization of the M. agalactiae liposoluble protein component, providing useful insights into its membrane organization.Mycoplasmas are the smallest and simplest prokaryotes capable of self-replication, being provided only with the minimal machinery required for survival. During evolution, they have regressively evolved from gram-positive bacteria by reduction of their genome to an essential minimum, economizing their structural elements, metabolic pathways, and genetic resources [1].Among other consequences, this cost-cutting strategy led to loss of the cell-wall component, and therefore to lack of a peptidoglycan "shell". Instead, sterols are incorporated into the lipid bilayer, providing resistance to rupture, but still allowing a certain flexibility of cell shape. Integral and associated membrane proteins are therefore directly exposed and act as the immediate bacterial interface, playing a major role in survival and pathogenesis [2,3]. Gathering informa