9.A.44 The Archaeocin/Halocin H4 (HalH4) Family
Archaeocins are ribosomally-synthesized antimicrobial peptides or proteins produced by Archaea. Halocins and sulfolobicins are produced by Archaea belonging to the order Halobacteriales (Euryarchaeota) and Sulfolobales (Crenarchaeota), respectively (Besse et al. 2015). One of the best characterized halocins is HalH4 from Haloferax mediterranei, the gene being found on the pHM300 megaplasmid. HalH4 is a 40 kDa protein with an N-terminal 46 aa leader peptide which is cleaved off leaving a 313 aa mature halocin. HalH4 uses the membrane as primary target and modifies its permeabillity, disrupting the ion gradients across the membrane. It may affect the passive H+ permeability specifically (Besse et al. 2015). Upon addition, sweiling followed by cell lysis occurs. It seems likely that it is a pore-former.