Mycobacterial porins are a group of transmembrane

beta-barrel In protein structures, a beta barrel is a beta 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 in many beta-barrels are ...

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'') and ...

, which allow hydrophilic nutrients to enter the bacterium. Mycobacterial porins--new channel proteins in unique outer membranes
by Michael Niederweis,

Molecular Microbiology Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including biomolecular synthesis, modification, mechanisms, and interactions. The study of chemical and physi ...

, 2003 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 Porins are beta barrel proteins that cross a cellular membrane and act as a pore, through which molecules can diffuse. Unlike other membrane transport proteins, porins are large enough to allow passive diffusion, i.e., they act as channels tha ...

located in the outer membrane of

Gram-negative bacteria Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...

. 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 ty ...

contains a

beta-sandwich Beta-sandwich, 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 protein ...

of immunoglobulin-like

topology In mathematics, topology (from the Greek language, Greek words , and ) is concerned with the properties of a mathematical object, geometric object that are preserved under Continuous function, continuous Deformation theory, deformations, such ...

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. Using nanopore sequencing, a single molecule of DNA or RNA can be sequenced without the ne ...

References

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