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Cryptochromes are evolutionarily related to the light-dependent DNA repair enzyme photolyase, serving as major regulators of circadian rhythms in insects and vertebrate animals. There are two types of cryptochromes in the animal kingdom: Drosophila-like CRYs that act as nonvisual photopigments linking circadian rhythms to the environmental light/dark cycle, and vertebrate-like CRYs that do not appear to sense light directly, but control the generation of circadian rhythms by acting as transcriptional repressors. Some animals have both types of CRYs, while others possess only one. Cryptochromes have two domains, the photolyase homology region (PHR) and an extended, intrinsically disordered C-terminus. While all animal CRYs share a high degree of sequence and structural homology in their PHR domains, the C-termini are divergent in both length and sequence identity. Recently, cryptochrome function has been shown to extend beyond its pivotal role in circadian clocks, participating in regulation of the DNA damage response, cancer progression and glucocorticoid signaling, as well as being implicated as possible magnetoreceptors. In this review, we provide a historical perspective on the discovery of animal cryptochromes, examine similarities and differences of the two types of animal cryptochromes and explore some of the divergent roles for this class of proteins. [ABSTRACT FROM AUTHOR]

Summary The myxovirus resistance (Mx) proteins are interferon-induced dynamin GTPases that can inhibit a variety of viruses. Recently, MxB, but not MxA, was shown to restrict HIV-1 by an unknown mechanism that likely occurs in close proximity to the host cell nucleus and involves the viral capsid. Here, we present the crystal structure of MxB and reveal determinants involved in HIV-1 restriction. MxB adopts an extended antiparallel dimer and dimerization, but not higher-ordered oligomerization, is critical for restriction. Although MxB is structurally similar to MxA, the orientation of individual domains differs between MxA and MxB, and their antiviral functions rely on separate determinants, indicating distinct mechanisms for virus inhibition. Additionally, MxB directly binds the HIV-1 capsid, and this interaction depends on dimerization and the N terminus of MxB as well as the assembled capsid lattice. These insights establish a framework for understanding the mechanism by which MxB restricts HIV-1. [ABSTRACT FROM AUTHOR]

The HIV-1 virion infectivity factor (Vif) targets the cellular cytidine deaminases APOBEC3G (A3G) and APOBEC3F (A3F) for degradation via the host ubiquitin-proteasome pathway. Vif recruits a cellular E3 ubiquitin ligase to polyubiquitinate A3G/F. The activity of Vif critically depends on the cellular core binding factor beta (CBFβ). In this study, we investigated the Vif-CBFβ interaction and the role of CBFβ in the E3 ligase assembly. Vif-CBFβ interaction requires an extensive region of Vif spanning most of its amino terminus and zinc finger region, and cullin 5 (Cul5) binding enhances the stability of the Vif-CBFβ interaction. Our results further demonstrate that CBFβ plays a critical role in facilitating Cul5 binding to the Vif/elongin B/elongin C complex. Vif, with or without bound substrate, is unable to bind Cul5 in the absence of CBFβ. These studies support the notion that CBFβ serves as a molecular chaperone to facilitate Vif-E3 ligase assembly. [ABSTRACT FROM AUTHOR]

Abstract: The Thiobacillus denitrificans genome contains two sequences corresponding to ATP sulfurylase (Tbd_0210 and Tbd_0874). Both genes were cloned and expressed protein characterized. The larger protein (Tbd_0210; 544 residues) possesses an N-terminal ATP sulfurylase domain and a C-terminal APS kinase domain and was therefore annotated as a bifunctional enzyme. But, the protein was not bifunctional because it lacked ATP sulfurylase activity. However, the enzyme did possess APS kinase activity and displayed substrate inhibition by APS. Truncated protein missing the N-terminal domain had <2% APS kinase activity suggesting the function of the inactive sulfurylase domain is to promote the oligomerization of the APS kinase domains. The smaller gene product (Tbd_0874; 402 residues) possessed strong ATP sulfurylase activity with kinetic properties that appear to be kinetically optimized for the direction of APS utilization and ATP+sulfate production, which is consistent with an enzyme that functions physiologically to produce inorganic sulfate. [Copyright &y& Elsevier]

Ketone bodies are bioactive metabolites that function as energy substrates, signaling molecules, and regulators of histone modifications. β-hydroxybutyrate (β-OHB) is utilized in lysine β-hydroxybutyrylation (Kbhb) of histones, and associates with starvation-responsive genes, effectively coupling ketogenic metabolism with gene expression. The emerging diversity of the lysine acylation landscape prompted us to investigate the full proteomic impact of Kbhb. Global protein Kbhb is induced in a tissue-specific manner by a variety of interventions that evoke β-OHB. Mass spectrometry analysis of the β-hydroxybutyrylome in mouse liver revealed 891 sites of Kbhb within 267 proteins enriched for fatty acid, amino acid, detoxification, and one-carbon metabolic pathways. Kbhb inhibits S-adenosyl-L-homocysteine hydrolase (AHCY), a rate-limiting enzyme of the methionine cycle, in parallel with altered metabolite levels. Our results illuminate the role of Kbhb in hepatic metabolism under ketogenic conditions and demonstrate a functional consequence of this modification on a central metabolic enzyme. [Display omitted] • Lysine β-hydroxybutyrylation (Kbhb) modifies non-histone proteins in liver and kidney • Starvation, ketogenic diet, and pharmacologically induced diabetes evoke Kbhb • LC-MS/MS identifies 891 Kbhb-modified peptides enriched for metabolic pathways • Kbhb inhibits the rate-limiting methionine cycle enzyme AHCY Lysine acylations are diverse and often metabolism-linked posttranslational modifications. Koronowski et al. find that dietary and disease states of ketogenesis evoke lysine β-hydroxybutyrylation (Kbhb) across the cellular proteome. In liver, a functional consequence of Kbhb is inhibition of the rate-limiting methionine cycle enzyme AHCY. [ABSTRACT FROM AUTHOR]

Summary The von Hippel-Lindau tumor suppressor protein (VHL) recruits a Cullin 2 (Cul2) E3 ubiquitin ligase to downregulate HIF-1α, an essential transcription factor for the hypoxia response. Mutations in VHL lead to VHL disease and renal cell carcinomas. Inhibition of this pathway to upregulate erythropoietin production is a promising new therapy to treat ischemia and chronic anemia. Here, we report the crystal structure of VHL bound to a Cul2 N-terminal domain, Elongin B, and Elongin C (EloC). Cul2 interacts with both the VHL BC box and cullin box and a novel EloC site. Comparison with other cullin E3 ligase structures shows that there is a conserved, yet flexible, cullin recognition module and that cullin selectivity is influenced by distinct electrostatic interactions. Our structure provides a structural basis for the study of the pathogenesis of VHL disease and rationale for the design of novel compounds that may modulate cullin-substrate receptor interactions. [ABSTRACT FROM AUTHOR]