The BlyA Holin Family
TC# 1.E.17
is a group of holin proteins that are approximately 55-70 amino acyl residues (aas) in length and exhibit one transmembrane segment (TMS). A representative list of the proteins belonging to the BlyA holin family can be found in th
Transporter Classification Database

BlyAB

The BlyA membrane protein and the BlyB soluble accessory protein are encoded on the conserved cp32 plasmid of ''

Borrelia burgdorferi ''Borrelia burgdorferi'' is a bacterial species of the spirochete class in the genus '' Borrelia'', and is one of the causative agents of Lyme disease in humans. Along with a few similar genospecies, some of which also cause Lyme disease, it mak ...

,'' which can be packaged into a

bacteriophage A bacteriophage (), also known informally as a ''phage'' (), is a duplodnaviria virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek φαγεῖν ('), meaning "to devour". Bacteri ...

particle. These two proteins had previously been proposed to comprise a

hemolysis Hemolysis or haemolysis (), also known by several other names, is the rupturing (lysis) of red blood cells (erythrocytes) and the release of their contents (cytoplasm) into surrounding fluid (e.g. blood plasma). Hemolysis may occur in vivo o ...

system, but Damman et al. (2000) provided evidence that BlyAB functions as a prophage-encoded holin system. BlyA promotes endolysin-dependent lysis of an induced lambda lysogen that is defective for the lambda holin S gene. The holin pores are generally stable and nonspecific, allowing endolysin access to the

peptidoglycan Peptidoglycan or murein is a unique large macromolecule, a polysaccharide, consisting of sugars and amino acids that forms a mesh-like peptidoglycan layer outside the plasma membrane, the rigid cell wall (murein sacculus) characteristic of most ba ...

. Introduction of the ''

'' ''blyAB'' locus into ''

Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...

'' produces a hemolytic phenotype that is dependent on the ''E. coli clyA (hlyE, sheA)'' gene
TC# 1.C.10.1.1
. Expression of ''blyA'' in ''E. coli'' causes damage to the ''E. coli'' cell envelope and a ''clyA''-dependent hemolytic phenotype, regardless whether ''blyB'' is present or absent. The expression of ''blyB'' in ''E. coli'', on the other hand, did not have obvious phenotypic effects. Transcriptional studies demonstrated that the ''clyA'' gene is not induced in ''E. coli'' cells expressing ''blyA''. Furthermore, protein analyses suggested that the impairment of the ''E. coli'' cell envelope by BlyA is responsible for the emergence of the hemolytic activity as it allows latent intracellular ClyA protein, derived from basal-level expression of the ''clyA'' gene, to leak into the medium and to lyse erythrocytes. These findings are compatible with the presumption that BlyA functions as a membrane-active holin.

Transport Reaction

The physiologically relevant transport reaction believed to be catalyzed by BlyA is:

Endolysin (in) → Endolysin (out)

References

{{CCBYSASource, sourcepath=http://tcdb.org/search/result.php?tc=1.E.17, sourcearticle=1.E.17 The BlyA Holin (BlyA Holin) Family, revision=699838558 Protein families Membrane proteins Transmembrane proteins Transmembrane transporters Transport proteins Integral membrane proteins Holins