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ATP-binding cassette (ABC) superfamily is one of the largest groups of primary active transporters that could be found in all kingdoms of life from bacteria to humans. In humans, ABC transporters can selectively transport a wide spectrum of substrates across membranes, thus playing a pivotal role in multiple physiological processes. In addition, due to the ability of exporting clinic therapeutics, some ABC transporters were originally termed multidrug resistance proteins. Increasing investigations of human ABC transporters in recent years have provided abundant information for elucidating their structural features, based on the structures at distinct states in a transport cycle. This review focuses on the recent progress in human ABC structural analyses, substrate binding specificities, and translocation mechanisms. We dedicate to summarize the common features of human ABC transporters in different subfamilies, and to discuss the possibility to apply the fast-developing techniques, such as cryogenic electron microscopy, and artificial intelligence-assisted structure prediction, for future studies., (© 2022 Wiley Periodicals LLC.)

Cyanophages, widespread in aquatic systems, are a class of viruses that specifically infect cyanobacteria. Though they play important roles in modulating the homeostasis of cyanobacterial populations, little is known about the freshwater cyanophages, especially those hypothetical proteins of unknown function. Mic1 is a freshwater siphocyanophage isolated from the Lake Chaohu. It encodes three hypothetical proteins Gp65, Gp66, and Gp72, which share an identity of 61.6% to 83%. However, we find these three homologous proteins differ from each other in oligomeric state. Moreover, we solve the crystal structure of Gp72 at 2.3 Å, which represents a novel fold in the α + β class. Structural analyses combined with redox assays enable us to propose a model of disulfide bond mediated oligomerization for Gp72. Altogether, these findings provide structural and biochemical basis for further investigations on the freshwater cyanophage Mic1., (© 2020 Wiley Periodicals, Inc.)

Yeast glutathione (GSH) reductase Glr1 is a dimeric flavo-oxidoreductase involved in cytoplasmic and mitochondrial redox regulatory systems. It reduces the oxidized GSH GSSG to the reduced form, GSH with NADPH as electron donor and FAD as coenzyme. Crystal structures and enzymatic mechanisms of GSH reductases from Escherichia coli and Homo sapiens have been well investigated, whereas the structural properties of yeast Glr1 remain unknown. Herein, we overexpressed Saccharomyces cerevisiae Glr1 in Pichia pastoris GS115 and determined its crystal structure at 2.40 A resolution. Although the overall structure and the active site are much conserved, obvious variety was found at the interface of Glr1 monomers when superimposed against the homolog from E. coli or human. The nonconserved C239 is exposed to the solvent and accessible to GSH or GSSG enriched in a microenvironment around the Glr1 molecules, leading to the partial and transient glutathionylation, as primarily identified from the 2Fo-Fc electron density map and further confirmed by biochemical assays. Meanwhile N278 at the vicinity of NADP-binding pocket was artificially glycosylated when heterogeneously overexpressed in P. pastoris. The highly motile oligosaccharide chain linked to N278 of the recombinant Glr1 interferes with the entry of NADPH, which results in a dramatic increase of Km for NAPDH and a significant decrease of turnover number, when compared with the native protein., (2007 Wiley-Liss, Inc.)

The protein product of the YGR205w gene of Saccharomyces cerevisiae was targeted as part of our yeast structural genomics project. YGR205w codes for a small (290 amino acids) protein with unknown structure and function. The only recognizable sequence feature is the presence of a Walker A motif (P loop) indicating a possible nucleotide binding/converting function. We determined the three-dimensional crystal structure of Se-methionine substituted protein using multiple anomalous diffraction. The structure revealed a well known mononucleotide fold and strong resemblance to the structure of small metabolite phosphorylating enzymes such as pantothenate and phosphoribulo kinase. Biochemical experiments show that YGR205w binds specifically ATP and, less tightly, ADP. The structure also revealed the presence of two bound sulphate ions, occupying opposite niches in a canyon that corresponds to the active site of the protein. One sulphate is bound to the P-loop in a position that corresponds to the position of beta-phosphate in mononucleotide protein ATP complex, suggesting the protein is indeed a kinase. The nature of the phosphate accepting substrate remains to be determined., (Copyright 2004 Wiley-Liss, Inc.)

The amino acid sequence of the heavy chain of Bombyx mori silk fibroin was derived from the gene sequence. The 5,263-residue (391-kDa) polypeptide chain comprises 12 low-complexity "crystalline" domains made up of Gly-X repeats and covering 94% of the sequence; X is Ala in 65%, Ser in 23%, and Tyr in 9% of the repeats. The remainder includes a nonrepetitive 151-residue header sequence, 11 nearly identical copies of a 43-residue spacer sequence, and a 58-residue C-terminal sequence. The header sequence is homologous to the N-terminal sequence of other fibroins with a completely different crystalline region. In Bombyx mori, each crystalline domain is made up of subdomains of approximately 70 residues, which in most cases begin with repeats of the GAGAGS hexapeptide and terminate with the GAAS tetrapeptide. Within the subdomains, the Gly-X alternance is strict, which strongly supports the classic Pauling-Corey model, in which beta-sheets pack on each other in alternating layers of Gly/Gly and X/X contacts. When fitting the actual sequence to that model, we propose that each subdomain forms a beta-strand and each crystalline domain a two-layered beta-sandwich, and we suggest that the beta-sheets may be parallel, rather than antiparallel, as has been assumed up to now., (Copyright 2001 Wiley-Liss, Inc.)