Ultrafiltration, a useful method for isolation of intermediates in native chemical ligation exemplified with the total synthesis of Sortase AΔN59.

In this paper, ultrafiltration was employed to facilitate the isolation of intermediates in native chemical ligation. Depending on the molecular weight cutoff of the membrane used, molecules with different sizes could be purified, separated, or concentrated by the ultrafiltration process. Total chemical synthesis of the polypeptide chain of the enzyme Sortase AΔN59 was used as an example of the application of ultrafiltration in chemical protein synthesis. Sortase A is a ligase that catalyzes transpeptidation reactions between proteins that have C-terminal LPXTG recognition sequence and Gly5- on the peptidoglycan of bacterial cell walls. Ultrafiltration technique facilitated synthesis of Sortase AΔN59 and was a promising tool in isolation of intermediates in native chemical ligation.

Total chemical synthesis of the enzyme sortase A(ΔN59) with full catalytic activity.

The enzyme sortase A is a ligase which catalyzes transpeptidation reactions.1, 2 Surface proteins, including virulence factors, that have a C terminal recognition sequence are attached to Gly5 on the peptidoglycan of bacterial cell walls by sortase A.1 The enzyme is an important anti-virulence and anti-infective drug target for resistant strains of Gram-positive bacteria.2 In addition, because sortase A enables the splicing of polypeptide chains, the transpeptidation reaction catalyzed by sortase A is a potentially valuable tool for protein science.3 Here we describe the total chemical synthesis of enzymatically active sortase A. The target 148 residue polypeptide chain of sortase AΔN59 was synthesized by the convergent chemical ligation of four unprotected synthetic peptide segments. The folded protein molecule was isolated by size-exclusion chromatography and had full enzymatic activity in a transpeptidation assay. Total synthesis of sortase A will enable more sophisticated engineering of this important enzyme molecule.

Synthesis and comparative properties of two amide-generating resin linkers for use in solid phase peptide synthesis.

Well-characterized resins of high purity are critical for effective solid phase peptide synthesis (SPPS). The quality of commercial (4-methyl)benzhydrylamine-resin (MBHA-resin), used for the synthesis of peptide amides, is not consistent and residual ketone functionalities are frequently present. Such ketone or aldehyde impurities lead to the formation of acylation-resistant deletion peptides in SPPS. To avoid these undesirable side reactions, we have optimized the preparation of two amide-generating linkers, which, in combination with aminomethyl-resin prepared directly from polystyrene resin, serve as alternatives to MBHA-resin for peptide amide synthesis. Then we have explored their comparative properties in SPPS. Use of sonication in reductive amination facilitated the synthesis of both benzhydrylamine (BHA) and MBHA linkers.