A newly mapped family of bacterial proteases trims peptides at one chosen site

Summary. Researchers at institutions in Shenzhen and Guangzhou, China, including Shenzhen Bay Laboratory and Sun Yat-sen University, reported in the Journal of the American Chemical Society, published online on 8 October, a clade of cyanobactin proteases that process a wide range of peptide substrates while keeping strict selectivity for their recognition sequence. The team found the clade with a sequence similarity network. Proteases that remove leader peptides are common in the biosynthesis of ribosomally synthesised and post-translationally modified peptides (RiPPs), but many known examples cut only after the core peptide has been modified, which limits their wider use. The authors showed that GusA, a representative member of the clade, can process structurally complex modified peptides and remove affinity tags from recombinant proteins.

Research context (RUO). Because GusA cleavage can expose an N-terminal cysteine, the authors used it to build chemically diversified, asymmetric phage-displayed macrocyclic peptide libraries, from which they identified ligands with nanomolar affinity for two protein targets, Keap1 and Bcl-xL. They also applied the approach to site-selective, multicolour labelling of proteins on the surface of mammalian cells, combined with bioorthogonal chemistry. The work was done with enzymes, phage libraries and cultured cells; it involves no animal or human data. For peptide chemists the appeal is a sequence-selective enzyme that accepts many substrates, adding a tool for tag removal, macrocycle library construction and protein labelling. Wider use will depend on other groups reproducing its selectivity in their own systems.