Page - (000241) - in Biomedical Chemistry: Current Trends and Developments

Wimley, 1994). The penaeidin class of peptides consist of a proline-rich N-terminus and a C-terminus containing six Cys residues engaged in three disulfide bridges (Destoumieux, 2000). The Pro-rich domain of penaeidin class AMPs confers the target specificity and antimicrobial activity of penaeidin (Cuthbertson, 2004). The carboxyl Cys-rich domain consists of an amphipathic helix linked to the upstream and downstream coils by two disulfide bonds. 3.1.3.1.4 Peptides Rich in Pro, Gly, His, Arg and Trp Residues This group includes AMPs such as apidaecins, short-chain Pro-rich peptides that may adopt a polyPro helical type II structure, possibly forming the structural basis to bind specific targets and confer antibacterial activity (Li, 2006). The mechanism of membrane action does not include the formation of pores but is energy-driven, resulting in a transporter-mediated model (Castle, 1999). As for the Pro-rich antimicrobial peptide class, the Gly rich peptides have variable sizes and do not show clear sequence consensus, apart from the high proportion of Gly in their primary sequence. These peptides are in general longer than AMP from other classes and between 25 to 50% of their amino acids are glycine. They have disordered structure in water but tend to self-order when in contact with artificial membranes (Bruston, 2007). Attacins are a group of six glycine-rich AMPs and can be grouped into four basic (A-D) and two acidic (E-F) peptides, probably derived from two attacin genes (Yi, 2014). Attacin inhibits the synthesis of outer membrane proteins of E. coli by blocking the transcription of the respective genes (Carlsson, 1991). This is presumably achieved by an indirect mechanism, where attacin binds to lipopolysaccharides (which serve as a receptor for attacin) but does not enter the bacterial cell (Carlsson, 1998). The archetypical Trp rich peptide is indolicin, which unlike the amphipathic alpha helical structure of the cecropin class of peptides, has a linear structure (no disulfide bridges) and no particular secondary structure in water. Some authors suggest that structural changes and strong membrane affinity are key to the antimicrobial activity of indolicin (Ladokhin & White, 2001). Trp-rich AMP sequences contain