Six-transmembrane helical domain (6-TMD) of the ABC subunit in the type 1 secretion systems (PrtD, LapB, HylB), and similar proteins
This group represents the six-transmembrane helical domain (6-TMD) of the ABC subunit in the type 1 secretion systems (T1SS), including PrtD, LapB, and HylB. T1SS are found in pathogenic Gram-negative bacteria (such as Escherichia coli, Vibrio cholerae or Bordetella pertussis) to export proteins (often proteases) across both inner and outer membranes to the extracellular medium. This is one of three proteins of the type 1 secretion apparatus. In the case of the Escherichia coli HlyA T1SS, these three proteins are HlyB (a dimeric ABC transporter), HlyD (MFP, oligomeric membrane fusion protein) and TolC (OMP, a trimeric oligomeric outer membrane protein). These three components assemble into a complex spanning both membranes and provide a channel for the translocation of unfolded polypeptides. In addition, PrtD is the integral membrane ATP-binding cassette component of the Erwinia chrysanthemi metalloprotease secretion system (PrtDEF). LabB is an inner-membrane transporter component of the LapBCE system that is required for the secretion of the LapA adhesion.
Comment:All members of this ABC transporter family contain 6 alpha-helices in each transmembrane domain (TMD) for a total of 12 TM segments in the complete transporter.
Jiyao W et al.(2023). "The conserved domain database in 2023.",