A backup porin induced when MspA, the major porin, is deleted. Probably forms a water-filled channel which favors the permeation of cations. There are about 2400 porins in wild-type, 800 in an mspA deletion and 150 in a double mspA-mspC deletion. A triple mspA-mspC-mspD deletion mutant has low but detectable channel activity. Different conductance values with maxima at 2.3 and 4.6 nanosiemens might be caused by a simultaneous reconstitution of MspB channels into the membrane or by the existence of different MspB conformations. Octamers. Probably forms 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 MspB with other Msp subunits form in vivo (By similarity). Not expressed in wild-type cells, it is induced in an mspA deletion mutant. Single deletion is viable, and shows no effects on glucose uptake. Belongs to the mycobacterial porin (TC 1.B.24) family. It is not clear if the data in PubMed:11309127 refer to MspB or MspC as they are nearly identical.