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Clustered regularly interspaced short palindromic repeats (CRISPR) in many prokaryotes functions as an adaptive immune system against mobile genetic elements. A heterologous ribonucleoprotein silencing complex composed of CRISPR-associated (Cas) proteins and a CRISPR RNA (crRNA) neutralizes the incoming mobile genetic elements. The type I and III silencing complexes commonly include a protein-helical backbone of several copies of identical subunits, for example, Cas7 in the type I silencing complex. In this study, we structurally characterized type I-B Cas7 (Csh2 from Thermobaculum terrenum; TterCsh2). The revealed crystal structure of TterCsh2 shows a typical glove-like architecture of Cas7, which consists of a palm, a thumb, and a finger domain. Csh2 proteins have 5 conserved sequence motifs that are arranged to form a presumable crRNA-binding site in the TterCsh2 structure. This crRNA binding site of TterCsh2 is structurally and potentially comparable to those observed in helix-forming Cas7 structures in other sub-types. Analysis of the reported Cas7 structures and their sequences suggests that Cas7s can be divided into at least two sub-classes. These data will broaden our understanding on the Cascade complex of CRISPR/Cas systems., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Baeyer-Villiger monooxygenase (BVMO) catalyzes insertion of an oxygen atom into aliphatic or cyclic ketones with high regioselectivity. The BVMOs from Parvibaculum lavamentivorans (BVMO Parvi ) and Oceanicola batsensis (BVMO Ocean ) are interesting because of their homologies, with >40% sequence identity, and reaction with the same cyclic ketones with a methyl moiety to give different products. The revealed BVMO Parvi structure shows that BVMO Parvi forms a two-domain structure like other BVMOs. It has two inserted residues, compared with BVMO Ocean , that form a bulge near the bound flavin adenine dinucleotide in the active site. Furthermore, this bulge is linked to a nearby α-helix via a disulfide bond, probably restricting access of the bulky methyl group of the substrate to this bulge. Another sequence motif at the entrance of the active site (Ala-Ser in BVMO Parvi and Ser-Thr in BVMO Ocean ) allows a large volume in BVMO Parvi . These minute differences may discriminate a substrate orientation in both BVMOs from the initial substrate binding pocket to the final oxygenation site, resulting in the inserted oxygen atom being in different positions of the same substrate., (Copyright © 2019 Elsevier Inc. All rights reserved.)

The tRNA methyltransferase J (TrmJ) and D (TrmD) catalyze the transferring reaction of a methyl group to the tRNA anticodon loop. They commonly have the N-terminal domain (NTD) and the C-terminal domain (CTD). Whereas two monomeric CTDs symmetrically interact with a dimeric NTD in TrmD, a CTD dimer has exhibited an asymmetric interaction with the NTD dimer in the presence of a product. The elucidated apo-structure of the full-length TrmJ from Zymomonas mobilis ZM4 shows a dimeric CTD that asymmetrically interacts with the NTD dimer, thereby distributing non-symmetrical potential charge on the both side of the protein surface. Comparison with the product-bound structures reveals a local re-orientation of the two arginine-containing loop at the active site, which interacts with the product. Further, the CTD dimers have diverse orientations compared to the NTD dimers, suggesting their flexibility. These data indicate that an asymmetric interaction between the NTD dimer and the CTD dimer is a common structural feature among TrmJ proteins, regardless of the presence of a substrate or a product., (Copyright © 2017 Elsevier Inc. All rights reserved.)