Recombinant Mycobacterium smegmatis Porin MspA (mspA)

Function

The major porin in this organism, forms a water-filled channel which favors the permeation of cations, amino acids, iron Fe(3+) and less efficiently phosphate. Does not transport Fe-ExoMS, the predominant siderophore. Plays a role in transport of beta-lactamase and hydrophilic fluoroquinolone antibiotics such as norfloxacin as well as chloramphenicol. There are about 2400 porins in wild-type, 800 in an mspA deletion and 150 in a double mspA-mspC deletion. Different conductance values with maxima at 2.3 and 4.6 nanosiemens might be caused by a simultaneous reconstitution of MspA channels into the membrane or by the existence of different MspA conformations

Subcellular Location

Cell outer membrane; Secreted, cell wall

Subunit

Forms very stable octamers. Isolated as a 100 kDa complex that can be reduced to monomers upon boiling in 80% dimethyl sulfoxide for 15 minutes. Structures show a goblet with the wide end on the exterior of the outer membrane and a central channel. It is not known if mixed oligomers of MspA with other Msp subunits form in vivo

• Niederweis M. et al. Cloning of the mspA gene encoding a porin from Mycobacterium smegmatis. — Mol. Microbiol. (1999)
• Fleischmann R.D. et al. PubMed: CI-ET8TSAB7T4FCA (OCT-)
• Deshayes C. et al. Interrupted coding sequences in Mycobacterium smegmatis: authentic mutations or sequencing errors? — Genome Biol. (2007)
• Gallien S. et al. Ortho-proteogenomics: multiple proteomes investigation through orthology and a new MS-based protocol. — Genome Res. (2009)
• Stahl C. et al. MspA provides the main hydrophilic pathway through the cell wall of Mycobacterium smegmatis. — Mol. Microbiol. (2001)
• Stephan J. et al. The growth rate of Mycobacterium smegmatis depends on sufficient porin-mediated influx of nutrients. — Mol. Microbiol. (2005)
• Mahfoud M. et al. Topology of the porin MspA in the outer membrane of Mycobacterium smegmatis. — J. Biol. Chem. (2006)
• Wolschendorf F. et al. Porins are required for uptake of phosphates by Mycobacterium smegmatis. — J. Bacteriol. (2007)