Halocin S8: a 36-Amino-Acid Microhalocin from the Haloarchaeal Strain S8a

Abstract

Halocin S8 is a hydrophobic microhalocin of 36 amino acids (3,580 Da) and is the first microhalocin to be described. This peptide antibiotic is unique since it is processed from inside a much larger, 33,962-Da pro-protein. Halocin S8 is quite robust, as it can be desalted, boiled, subjected to organic solvents, and stored at 4°C for extended periods without losing activity. The complete amino acid sequence of halocin S8 was obtained first by Edman degradation of the purified protein and verified from the halS8 gene: H 2 N-S-D-C-N-I-N-S-N-T-A-A-D-V-I-L-C-F-N-Q-V-G-S-C-A-L-C-S-P-T-L-V-G-G-P-V-P-COOH.The halS8 gene is encoded on an ϳ200-kbp megaplasmid and contains a 933-bp open reading frame, of which 108 bp are occupied by halocin S8. Both the halS8 promoter and the "leaderless" halS8 transcript are typically haloarchaeal. Northern blot analysis revealed three halS8 transcripts: two abundant and one minor. Inspection of the 3 end of the gene showed only a single, weak termination site (5-TTTAT-3), suggesting that some processing of the larger transcripts may be involved. Expression of the halS8 gene is growth stage dependent: basal halS8 transcript levels are present in low concentrations during exponential growth but increase ninefold during the transition to stationary phase. Initially, halocin activity parallels halS8 transcript levels very closely. However, when halocin activity plateaus, transcripts remain abundant, suggesting inhibition of translation at this point. Once the culture enters stationary phase, transcripts rapidly return to basal levels.

Subunit Topology of Two 20S Proteasomes from Haloferax volcanii

“…The T7 terminator and ribosome binding sequence from pET24b were included to facilitate protein synthesis. Although leaderless transcripts have been described for the haloarchaea (3,4,7,11,28,29), the 3Ј-end 16S rRNA sequences of E. coli and H. volcanii are highly related (HO-AUUCCUCCACUAGGUUGG for E. coli [5] and HO-UC-CUCCACUAGGUCGG for H. volcanii [accession no. AB074566]).…”

Bacteriocins of Aquatic Microorganisms and Their Potential Applications in the Seafood Industry

“…Halocins are located on megaplasmids (or minichromosomes). Halocins H4 and S8 are located on ~300 kbp and ~200 kbp plasmids, respectively (Cheung et al, 1997;Price & Shand, 2000). Their activity is usually detected at the late exponential to early stationary growth phase (Cheung et al, 1997;Price & Shand, 2000).…”

Microbial defense systems in foods and feeds

“…The only characterized member is from the halocin family produced by halobacteria (Cheung et al, 1997;Shand et al, 1998). S8 is the first discovered halocin and is composed of a short hydrophobic peptide with 36 amino acids, this is derived from larger pro-protein of 34 KDa (Price and Shand, 2000). The gene for Halocin S8 is located on a megaplasmid and is very hardy; as it can be desalted, boiled, resistant to to organic solvents, and can be stored at 4±ºC for long period without loss of activity.…”