Mycobacterial porins are a group of transmembrane

beta-barrel In protein structures, a beta barrel (β barrel) is a beta sheet (β sheet) composed of tandem repeats that twists and coils to form a closed toroidal structure in which the first strand is bonded to the last strand (hydrogen bond). Beta-strands ...

proteins produced by

mycobacteria ''Mycobacterium'' is a genus of over 190 species in the phylum Actinomycetota, assigned its own family, Mycobacteriaceae. This genus includes pathogens known to cause serious diseases in mammals, including tuberculosis ('' M. tuberculosis'') a ...

, which allow hydrophilic nutrients to enter the bacterium. They are located in the impermeable mycobacterial outer membrane, or mycomembrane of fast-growing mycobacteria. The mycomembrane is unique and composed of very-long chain fatty acids, mycolic acids. These proteins are structurally different from the typical porins located in the outer membrane of

Gram-negative bacteria Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the Crystal violet, crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelo ...

. For example, the MspA protein forms a tightly interconnected octamer with eight-fold rotation symmetry that resembles a goblet and contains a central channel. Each

protein subunit In structural biology, a protein subunit is a polypeptide chain or single protein molecule that assembles (or "''coassembles''") with others to form a protein complex. Large assemblies of proteins such as viruses often use a small number of t ...

contains a

beta-sandwich Beta-sandwich or β-sandwich domains consisting of 80 to 350 amino acids occur commonly in proteins. They are characterized by two opposing antiparallel beta sheets (β-sheets). The number of strands found in such domains may differ from one prote ...

of immunoglobulin-like

topology Topology (from the Greek language, Greek words , and ) is the branch of mathematics concerned with the properties of a Mathematical object, geometric object that are preserved under Continuous function, continuous Deformation theory, deformat ...

and a beta-ribbon arm that forms an oligomeric transmembrane

. MspA has biotechnological applications, most notably in

nanopore sequencing Nanopore sequencing is a third generation approach used in the sequencing of biopolymers — specifically, polynucleotides in the form of DNA or RNA. Nanopore sequencing allows a single molecule of DNA or RNA be sequenced without PCR amplif ...

References

Protein domains Outer membrane proteins {{membrane-protein-stub