What is "holin"

n. (context biology English) Any of a diverse group of small proteins produced by dsDNA bacteriophages in order to trigger and control the degradation of the host's cell wall at the end of the lytic cycle.

Holins are a diverse group of small proteins produced by dsDNA bacteriophages in order to trigger and control the degradation of the host's cell wall at the end of the lytic cycle. Holins form pores in the host's cell membrane, allowing lysins to reach and degrade peptidoglycan, a component of bacterial cell walls. Holins have been shown to regulate the timing of lysis with great precision. Over 50 unrelated gene families encode holins, making them the most diverse group of proteins with common function. Together with lysins, holins are being studied for their potential use as antibacterial agents.

While canonical holins act by forming large pores, pinholins such as the S protein of lambdoid phage 21 act by forming heptameric channels that depolarize the bacterial membrane. They are associated with SAR endolysins, which remain inactive in the periplasm prior to the depolarization of the membrane.

Viruses that infect eukaryotic cells may use similar proteins called viroporins to permeabilize the host's membrane.