Selective Bi-directional Amide Bond Cleavage ofN-Methylcysteinyl Peptide

Sunflower Trypsin Inhibitor-1 (SFTI-1): Sowing Seeds in the Fields of Chemistry and Biology

Nature-derived cyclic peptides have proven to be a vast source of inspiration for advancing modern pharmaceutical design and synthetic chemistry. The focus of this Review is sunflower trypsin inhibitor-1 (SFTI-1), one of the smallest disulfide-bridged cyclic peptides found in nature. SFTI-1 has an unusual biosynthetic pathway that begins with a dual-purpose albumin precursor and ends with the production of a high-affinity serine protease inhibitor that rivals other inhibitors much larger in size. Investigations on the molecular basis for SFTI-1's rigid structure and adaptable function have planted seeds for thought that have now blossomed in several different fields. Here we survey these applications to highlight the growing potential of SFTI-1 as a versatile template for engineering inhibitors, a prototypic peptide for studying inhibitory mechanisms, a stable scaffold for grafting bioactive peptides, and a model peptide for evaluating peptidomimetic motifs and platform technologies.

Amide Bond Activation of Biological Molecules

Amide bonds are the most prevalent structures found in organic molecules and various biomolecules such as peptides, proteins, DNA, and RNA. The unique feature of amide bonds is their ability to form resonating structures, thus, they are highly stable and adopt particular three-dimensional structures, which, in turn, are responsible for their functions. The main focus of this review article is to report the methodologies for the activation of the unactivated amide bonds present in biomolecules, which includes the enzymatic approach, metal complexes, and non-metal based methods. This article also discusses some of the applications of amide bond activation approaches in the sequencing of proteins and the synthesis of peptide acids, esters, amides, and thioesters.

Antimicrobial Peptides from Plants

Plant antimicrobial peptides (AMPs) have evolved differently from AMPs from other life forms. They are generally rich in cysteine residues which form multiple disulfides. In turn, the disulfides cross-braced plant AMPs as cystine-rich peptides to confer them with extraordinary high chemical, thermal and proteolytic stability. The cystine-rich or commonly known as cysteine-rich peptides (CRPs) of plant AMPs are classified into families based on their sequence similarity, cysteine motifs that determine their distinctive disulfide bond patterns and tertiary structure fold. Cystine-rich plant AMP families include thionins, defensins, hevein-like peptides, knottin-type peptides (linear and cyclic), lipid transfer proteins, α-hairpinin and snakins family. In addition, there are AMPs which are rich in other amino acids. The ability of plant AMPs to organize into specific families with conserved structural folds that enable sequence variation of non-Cys residues encased in the same scaffold within a particular family to play multiple functions. Furthermore, the ability of plant AMPs to tolerate hypervariable sequences using a conserved scaffold provides diversity to recognize different targets by varying the sequence of the non-cysteine residues. These properties bode well for developing plant AMPs as potential therapeutics and for protection of crops through transgenic methods. This review provides an overview of the major families of plant AMPs, including their structures, functions, and putative mechanisms.