An accessory sec locus of Streptococcus gordonii is required for export of the surface protein GspB and for normal levels of binding to human platelets

Mol Microbiol. 2002 May;44(4):1081-94. doi: 10.1046/j.1365-2958.2002.02949.x.


The translocation of proteins across the bacterial cell membrane is carried out by highly conserved components of the Sec system. Most bacterial species have a single copy of the genes encoding SecA and SecY, which are essential for viability. However, Streptococcus gordonii strain M99 encodes SecA and SecY homologues that are not required for viability or for the translocation of most exported proteins. The genes (secA2 and secY2) reside in a region of the chromosome required for the export of GspB, a 286 kDa cell wall-anchored protein. Loss of GspB surface expression is associated with a significant reduction in the binding of M99 to human platelets, suggesting that it may be an adhesin. Genetic analyses indicate that M99 has a second, canonical SecA homologue that is essential for viability. At least two other Gram-positive species, Streptococcus pneumoniae and Staphylococcus aureus, encode two sets of SecA and SecY homologues. One set is more similar to SecA and SecY of Escherichia coli, whereas the other set is more similar to SecA2 and SecY2 of strain M99. The conserved organization of genes in the secY2-secA2 loci suggests that, in each of these Gram-positive species, SecA2 and SecY2 may constitute a specialized system for the transport of a very large serine-rich repeat protein.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenosine Triphosphatases / chemistry
  • Adenosine Triphosphatases / genetics
  • Adenosine Triphosphatases / metabolism
  • Adhesins, Bacterial / genetics
  • Adhesins, Bacterial / metabolism
  • Amino Acid Sequence
  • Bacterial Adhesion*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Base Sequence
  • Blood Platelets / microbiology*
  • Blotting, Western
  • Cell Wall / metabolism
  • Chromosomes, Bacterial
  • Escherichia coli Proteins / chemistry
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / metabolism
  • Gene Order
  • Genes, Bacterial / genetics*
  • Humans
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Membrane Transport Proteins / chemistry
  • Membrane Transport Proteins / genetics
  • Membrane Transport Proteins / metabolism
  • Molecular Sequence Data
  • Protein Transport
  • SEC Translocation Channels
  • SecA Proteins
  • Sequence Homology, Amino Acid
  • Streptococcus / cytology
  • Streptococcus / genetics*
  • Streptococcus / growth & development
  • Streptococcus / physiology*


  • Adhesins, Bacterial
  • Bacterial Proteins
  • Escherichia coli Proteins
  • Membrane Proteins
  • Membrane Transport Proteins
  • SEC Translocation Channels
  • SecY protein, E coli
  • Adenosine Triphosphatases
  • SecA Proteins

Associated data

  • GENBANK/AY007502
  • GENBANK/AY028381
  • GENBANK/AY028382