IM Proteome Lopez2005Lai2004


78 proteins have been identified in inner membrane preparations by 2D-gel fractionation and MS identification of many protein isoform spots:
Lopez-Campistrous (2005) and Lai (2004)


As part of a determination of the total (cytosolic, periplasmic, inner and outer membrane-localized) E. coli proteome, Lopez-Campistrous et al. identified inner membrane proteins of E. coli K-12 under at least one of two growth conditions using mass spectrometry after separation with two-dimensional gel electrophoresis.

76 proteins are localized to the inner membrane, as identified in Supplementary Table 3 of Lopez-Campistrous( 2005). Unlike the IMemProt, the IM Proteome proteins listed here are not all predicted to have membrane spanning regions or to be integral membrane proteins.

Many of these IM-localized proteins bind to integral membrane proteins or have single membrane spanning domains predicted. In fact, only 7/738 IMemProts were identified among the 78 IM Proteome proteins listed here: cld, msbA, mtlA, pntB, sohB, tsr and yqiK.

The 2D gel step may have enriched for membrane-associated proteins with soluble domains, including some lipoproteins (LipoProt) excluded from the IMemProt classification. Some proteins with known or suspected cytoplasmic, periplasmic and outer membrane locations were assigned an inner membrane location in this study. This may result from some proteins sticking to inner membranes during sample preparation or from cross-contamination of cell fractions. However, it is likely that most, if not all, of these proteins do associate with the inner membrane, or inner membrane complexes, in vivo, in physiologiocally relevant interactions.

In a second study using 2D_MS to identify membrane proteins, Lai (2004) examined total membrane preparations from minicells and rods to look for proteins with polar and septal localization. OmpW was identified as an outer membrane protein localized to the cell poles and the membrane protein YiaF was identified as having a polar and septal location bias.

The five inner membrane proteins identified by Lai (2004) include AtpA, YiaF and AcrA, all also localized to the IM by Lopez-Campistrous (2005), IMemProt_E protein AtpB, and FtsZ, an inner membrane associated protein bound to the cytoplasmic side that was identified by Lopez-Campistrous (2005) as a periplasmic protein, perhaps artifactually. FtsZ and AtpB are included in this subTopic based on the Lai (2004) results for a total of 78 IMem_Loc_2DMS proteins.