The C-terminal part of the surface-associated protein MopE of the methanotroph Methylococcus capsulatus (Bath) is secreted into the growth medium

Abstract

A protein with an apparent molecular mass of 46 kDa was detected as the major polypeptide in the culture medium of the biotechnologically important methanotrophic bacterium Methylococcus capsulatus (Bath). The protein cross-reacted with polyclonal antibodies raised against the outer-membrane-associated protein MopE. The antiserum was used to identify a positive clone from a lambda gt11 library. The nucleotide sequence determined for the clone demonstrated that MopE and the secreted protein are encoded by the same gene, and that the secreted protein represents an N-terminally truncated form of MopE. By using monospecific antibodies against MopE in immunogold electron microscopy, the protein was localized at the cell surface and cell periphery. The mopE gene was expressed in Escherichia coli. The MopE protein synthesized was found in the periplasmic space of E. coli. No protein with sequence similarity over the entire length of MopE was detected in the databases, but some sequence similarity to the copper-repressible CorA protein of the methanotroph Methylomicrobium albus (Berson and Lidstrom 1997) was observed for the C-terminal region of MopE.

CorA Is a Copper Repressible Surface-Associated Copper(I)-Binding Protein Produced in Methylomicrobium album BG8

“…CorA shares significant sequence similarity to the M. capsulatus Bath protein MopE and the recently described MEALZv2_1030034 protein isolated from Methylomicrobium alcaliphilum 20Z (Fig. S1) [20], [24]. CorA is smaller compared to MopE, and the sequence similarity is therefore restricted to the MopE C-terminal part, i.e.…”

The Surface-Associated and Secreted MopE Protein of Methylococcus capsulatus (Bath) Responds to Changes in the Concentration of Copper in the Growth Medium

“…This is in contrast to the extracellular copper-binding peptides, which seem to be associated with expression of pMMO and are less abundant in the spent medium of sMMO-expressing cells (4), and it is tempting to speculate that M. capsulatus may have evolved multiple copper acquisition systems that operate at different copper concentrations. However, except for the CorA protein (1), MopE does not show sequence similarity to other proteins in the databases and the primary amino acid sequence of MopE does not appear to contain conserved copper-binding motifs (7). Thus, the ability of MopE to bind copper or coppercontaining compounds remains to be investigated further by detailed biochemical studies.…”

Quantitative Proteomic Analysis of Metabolic Regulation by Copper Ions in Methylococcus capsulatus (Bath)

“…We have also observed the surface-associated protein precursor (MopE) (L/H ϭ 6.3) when the cells were grown at 0 M copper concentration. The C-terminal of this protein has been reported to be secreted by M. capsulatus (Bath) into the growth media, with the possibility of some catalytic and/or copper binding function (26), but this protein was not found in enriched copper-containing environments. Peptidoglycan-associated lipoprotein (L/H ϭ 3.39) is thought to play a role in Gramnegative bacterial envelope integrity.…”