Homemade cofactors: self-processing in galactose oxidase

Comparative structural analysis provides new insights into the function of R2-like ligand-binding oxidase

R2‐like ligand‐binding oxidase (R2lox) is a ferritin‐like protein that harbours a heterodinuclear manganese–iron active site. Although R2lox function is yet to be established, the enzyme binds a fatty acid ligand coordinating the metal centre and catalyses the formation of a tyrosine–valine ether cross‐link in the protein scaffold upon O₂ activation. Here, we characterized the ligands copurified with R2lox by mass spectrometry‐based metabolomics. Moreover, we present the crystal structures of two new homologs of R2lox, from Saccharopolyspora erythraea and Sulfolobus acidocaldarius, at 1.38 Å and 2.26 Å resolution, respectively, providing the highest resolution structure for R2lox, as well as new insights into putative mechanisms regulating the function of the enzyme.

Unusual post-translational protein modifications: the benefits of sophistication

This review summarizes the “seemingly bizarre”, yet naturally occurring, covalent non-disulphide cross-links in enzymatic and scaffolding proteins and their functions.

A diiron protein autogenerates a valine-phenylalanine cross-link

All known internal covalent cross-links in proteins involve functionalized groups having oxygen, nitrogen, or sulfur atoms present to facilitate their formation. Here, we report a carbon-carbon cross-link between two unfunctionalized side chains. This valine-phenyalanine cross-link, produced in an oxygen-dependent reaction, is generated by its own carboxylate-bridged diiron center and serves to stabilize the metallocenter. This finding opens the door to new types of posttranslational modifications, and it demonstrates new catalytic potential of diiron centers.

What's in a covalent bond? On the role and formation of covalently bound flavin cofactors

Many enzymes use one or more cofactors, such as biotin, heme, or flavin. These cofactors may be bound to the enzyme in a noncovalent or covalent manner. Although most flavoproteins contain a noncovalently bound flavin cofactor (FMN or FAD), a large number have these cofactors covalently linked to the polypeptide chain. Most covalent flavin-protein linkages involve a single cofactor attachment via a histidyl, tyrosyl, cysteinyl or threonyl linkage. However, some flavoproteins contain a flavin that is tethered to two amino acids. In the last decade, many studies have focused on elucidating the mechanism(s) of covalent flavin incorporation (flavinylation) and the possible role(s) of covalent protein-flavin bonds. These endeavors have revealed that covalent flavinylation is a post-translational and self-catalytic process. This review presents an overview of the known types of covalent flavin bonds and the proposed mechanisms and roles of covalent flavinylation.