Laccases (EC 1.10.3.2) are multicopper oxidoreductases acting on diphenols and related substances. Laccases are highly important for biotechnology and environmental remediation. These enzymes contain mononuclear one T2 copper ion and two T3 copper ions (Cu3_α and Cu3_β), which form the so-called trinuclear center (TNC). Along with the typical three-domain laccases Bacteria produce two-domain (2D) enzymes, which are active at neutral and basic pH, thermostable, and resistant to inhibitors. In this work we present the comparative analysis of crystal structures and catalytic properties of recombinant 2D laccase from Streptomyces griseoflavus Ac-993 (SgfSL) and its four mutant forms with replacements of two amino acid residues, located at the narrowing of the presumable T3-solvent tunnels. We obtained inactive enzymes with substitutions of His165, with Phe, and Ile170 with Ala or Phe. His165Ala variant was more active than the wild type. We suggest that His165 is a “gateway” at the O₂-tunnel leading from solvent to the Cu3_β of the enzyme. The side chain of Ile170 could be indirectly involved in the coordination of copper ions at the T3 center by maintaining the position of the imidazole ring of His157 that belongs to the first coordination sphere of Cu3_α.

The Sm and Sm-like proteins are widely distributed among bacteria, archaea and eukarya. They participate in many processes related to RNA-processing and regulation of gene expression. While the function of the bacterial Lsm protein Hfq and eukaryotic Sm/Lsm proteins is rather well studied, the role of Lsm proteins in Archaea is investigated poorly. In this work, the RNA-binding ability of an archaeal Hfq-like protein from Methanococcus jannaschii has been studied by X-ray crystallography, anisotropy fluorescence and surface plasmon resonance. It has been found that MjaHfq preserves the proximal RNA-binding site that usually recognizes uridine-rich sequences. Distal adenine-binding and lateral RNA-binding sites show considerable structural changes as compared to bacterial Hfq. MjaHfq did not bind mononucleotides at these sites and would not recognize single-stranded RNA as its bacterial homologues. Nevertheless, MjaHfq possesses affinity to poly(A) RNA that seems to bind at the unstructured positive-charged N-terminal tail of the protein.

Protein synthesis on ribosomes is considered the main process in cell life. Regulation of ribosomal protein gene expression plays an important role in the balanced synthesis of proteins and RNA in ribosomal biogenesis. This review is focused on some features of autoregulation of ribosomal protein synthesis in prokaryotes. Inhibition of the synthesis of ribosomal proteins encoded by 12 operons by mechanisms of competition , “entrapment”, and retroregulation are discussed. Examples of regulation of protein synthesis by individual ribosomal proteins and their complexes are presented.

Laccase belongs to the family of copper-containing oxidases. A study was made of the mechanism that sustains the incorporation of copper ions into the T2/T3 centers of recombinant two-domain laccase ...