Motility protein B also known as MotB is a bacterial

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

that is encoded by the ''motB''

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

. It's a component of the flagellar motor. More specifically, MotA and MotB makes the

stator The stator is the stationary part of a rotary system, found in electric generators, electric motors, sirens, mud motors, or biological rotors (such as bacterial flagella or ATP synthase). Energy flows through a stator to or from the rotat ...

of a flagellum and surround the rotor as a ring of about 8-10 particles. MotA and MotB are

integral membrane protein An integral, or intrinsic, membrane protein (IMP) is a type of membrane protein that is permanently attached to the biological membrane. All transmembrane proteins can be classified as IMPs, but not all IMPs are transmembrane proteins. IMPs comp ...

s. While both MotA and MotB surround the MS ring, MotB also anchors MotA to cell wall peptidoglycan. These two proteins form pores that harvest energy for flagellar mechanical movement by proton motive force (PMF) across the membrane. Cellular metabolic processes such as the electron transport chain move protons outside the cell, creating more protons and more positive charge in the extracellular space. When the protons flow back into the cell through MotA and MotB along concentration and charge gradients, they release energy that is used for flagellar rotation. The speed of the flagellar motor is dependent on the magnitude of the PMF acting on MotA and MotB.

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