MSP nanopores and procedures

Porin Mycobacterium smegmatis (Msp) having a lobby and a constriction zone that define a tunnel, wherein the Msp comprises a mutant msPa comprising a mutation in the 90, 91 and 93 positions, wherein the mutation in the position 90 is D90N, the mutation at position 91 is D91N, and the mutation at position 93 is D93N.