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.
Halocin H4 precursor protein of 359 aas with one TMS. The mature HalH4 lacks the N-terminal 46 aas and has 313 aas. Causes swelling and lysis of the target cell (Besse et al. 2015).
HalH4 of Haloferax mediterranei (Halobacterium mediterranei)
HalH4 homologue of 278 aas and 1 TMS.
HalH4 homologue of Natrialba aegyptia
Uncharacterized protein of 312 aas and 1 TMS.
UP of Natrialba magadii (Natronobacterium magadii)
Uncharacterized protein of 316 aa
UP of Methanococcoides burtonii
Uncharacterized protein of 106 aas
UP of Methanosarcina acetivorans