Man Pan

Irreversible Site-Specific Hydrazinolysis of Proteins by Use of Sortase†

Sortase-mediated hydrazinolysis of proteins with hydrazine or its derivatives was developed for the production of recombinant protein hydrazides. This process provides an alternative approach for protein semisynthesis through the use of recombinant protein hydrazides as thioester surrogates. It also provides an alternative method for C-terminal modification of proteins with functional units as well as for the preparation of C-to-C fusion proteins.

Quasi-Racemic X-ray Structures of K27-Linked Ubiquitin Chains Prepared by Total Chemical Synthesis

Quasi-racemic crystallography has been used to determine the X-ray structures of K27-linked ubiquitin (Ub) chains prepared through total chemical synthesis. Crystal structures of K27-linked di- and tri-ubiquitins reveal that the isopeptide linkages are confined in a unique buried conformation, which provides the molecular basis for the distinctive function of K27 linkage compared to the other seven Ub chains. K27-linked di- and triUb were found to adopt different structural conformations in the crystals, one being symmetric whereas the other triangular. Furthermore, bioactivity experiments showed that the ovarian tumor family de-ubiquitinase 2 significantly favors K27-linked triUb than K27-linked diUb. K27-linked triUb represents the so-far largest chemically synthesized protein (228 amino acids) that has been crystallized to afford a high-resolution X-ray structure.

Synthesis of and Specific Antibody Generation for Glycopeptides with Arginine N-GlcNAcylation†

As a unique and unappreciated protein posttranslational modification, arginine N-glycosylation was recently discovered to play an important role in the process that bacteria counteract host defenses. To provide chemical tools for further proteomic and biochemical studies on arginine N-glycosylation, we report the first general strategy for a rapid and cost-effective synthesis of glycopeptides carrying single or multiple arginine N-GlcNAcyl groups. These glycopeptides were successfully utilized to generate the first antibodies that can specifically recognize arginine N-GlcNAcylated peptides or proteins in a sequence-independent manner.

A semisynthetic Atg3 reveals that acetylation promotes Atg3 membrane binding and Atg8 lipidation

Acetylation of Atg3 regulates the lipidation of the protein Atg8 in autophagy. The molecular mechanism behind this important biochemical event remains to be elucidated. We describe the first semi-synthesis of homogeneous K19/K48-diacetylated Atg3 through sequential hydrazide-based native chemical ligation. In vitro reconstitution experiments with the semi-synthetic proteins confirm that Atg3 acetylation can promote the lipidation of Atg8. We find that acetylation of Atg3 enhances its binding to phosphatidylethanolamine-containing liposomes and to endoplasmic reticulum, through which it promotes the lipidation process.

Total synthesis of mambalgin-1/2/3 by two-segment hydrazide-based native chemical ligation

Mambalgins are a class of 57‐residue polypeptide toxins isolated from the venom of the African mamba. They exhibit potent analgesic effects by inhibiting the acid‐sensing ion channels. Classified as members of the family of three‐finger toxins, mambalgins contain four pairs of disulfide bridges that help to stabilize the three‐finger scaffold. Here, we report the chemical synthesis of functional mambalgin‐1/2/3 by using one‐step two‐segment hydrazide‐based native chemical ligation. The two‐segment ligation approach reported here may enable efficient production of mambalgin toxins. These synthetic mambalgins are useful compounds for development of diagnostic or therapeutic reagents. Copyright

A Highly Efficient Synthesis of Polyubiquitin Chains

Abstract A robust, microwave‐assisted, highly efficient, solid‐phase peptide synthesis method for preparing isopeptide‐linked 62‐mer and 76‐mer isoubiquitins and polyubiquitin is developed. The strategy avoids the use of costly resins and pseudoprolines, and the isopeptide‐linked building blocks can be assembled with high initial purity within 1 day. All seven diubiquitins are successfully synthesized on a multi‐milligram scale; a four‐segment, three‐ligation method is used to obtain a K33‐/K11‐linked mixed triubiquitin in excellent yield. Circular dichroism and crystallographic analyses are used to verify the structures of the well‐folded, synthetic polyubiquitin chains. The facile synthetic strategy is expected to be generally applicable for the rapid synthesis of isopeptide‐linked isoUbs and to pave the way for the study of longer polyubiquitin chains.

Chemical Synthesis of Natural Polyubiquitin Chains through Auxiliary-Mediated Ligation of an Expressed Ubiquitin Isomer

An efficient method for the assembly of polyUb chains using auxiliary-modified Ub isomers is reported. This strategy takes advantages of auxiliary-mediated native chemical ligation between the distal Ub C-terminal hydrazide and the auxiliary of proximal Ub. Using removable protecting groups, Lys48-linked and Lys6-linked tri-Ub and even a mixed-linkage Lys6, Lys48-linked triUb in multimilligram quantities was made. These results demonstrate that this strategy yields natural polyubiquitin chains of desired length and linkage by using Ub isomer.