M. smegmatis porin, MspA (cation selective due to a high density of negative charges in the constriction zone, but it transports glucose, serine, hydrophilic β-lactams and (slowly) phosphate (Wolschendorf et al., 2007). The MspC paralogue appears to have the same specificity as MspA. Both can also transport fluoroquinolones and chloramphenicol but not the larger erythromycin, kanamycin, and vancomycin (Danilchanka et al., 2008). Also allows uptake of ferric iron (Jones and Niederweis, 2010). The 3-d structure is known (PDB#1UUN). It is a β-barrel with N- and C-termini of their single hairpins on the outside, and their chains run in an anti-clockwise direction around the central pore. Both of these characteristics are opposite in most gram-negative bacterial β-barrels (Remmert et al., 2010).  Forms homo-octameric voltage-gated nanopores where each subunit contributes 2 TMSs to the 16 stranded β-barrel (Faller et al. 2004; Rodrigues et al. 2011; Pavlenok et al. 2012) that can be used for nanopore sequencing (Laszlo et al. 2016). MspA is a biosensor for DNA sequencing and many other applications by enabling the production of pores with distinct subunit mutations and pore diameters (Pavlenok et al. 2022). See Samineni et al. 2023 for details of this and other pore-forming proteins.  MspA forms pores in the outer mycobacterial membrane (Samineni et al. 2023).<Pavlenok et al. 2012) that can be used for nanopore sequencing (Laszlo et al. 2016). MspA is a biosensor for DNA sequencing and many other applications by enabling the production of pores with distinct subunit mutations and pore diameters (Pavlenok et al. 2022). See Samineni et al. 2023 for details of this and other pore-forming proteins.  MspA forms pores in the outer mycobacterial membrane (Samineni et al. 2023).