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ADP-ribosylation factors (ARFs) are small (21 kDa), monomeric GTPases that are important regulators of membrane traffic. When membrane bound, they recruit soluble adaptors to membranes and trigger the assembly of coating complexes involved in cargo selection and vesicular budding. N-myristoylation is a conserved feature of all ARF proteins that is required for its biological functions, although the...
Phosphorylase kinase (PhK) coordinates hormonal and neuronal signals to initiate the breakdown of glycogen. The enzyme catalyzes the phosphorylation of inactive glycogen phosphorylase b (GPb), resulting in the formation of active glycogen phosphorylase a. We present a 9.9 Å resolution structure of PhK heterotetramer (αβγδ) 4 determined by cryo-electron microscopy single-particle reconstruction...
Pseudokinases are an intriguing group inside the large protein kinase family. Lacking the highly conserved catalytic machinery, they can be still important for multiple functions in living cells. The structures of two pseudokinases VRK3 (Scheeff et al., 2009) and ROP2 (Labesse et al., 2009), presented in this issue of Structure, shed light on the internal machinery of these unique molecules. Structural...
G-protein-coupled receptors (GPCRs) are the largest family of proteins in the human genome. Within the last year, we have witnessed a relative explosion in the amount of structural information available for the GPCR family with two new structures of opsin in the presence and absence of transducin peptide, four new structures of β-adrenergic receptors, and a recent structure of the human adenosine...
In this issue, Sharon et al. (2009) determined the subunit organization of the COP9 signalosome by mass spectrometry. The structural features uncovered from this analysis are consistent with the multifunctionality of the complex and suggest tantalizing new clues about the inner workings of the CSN.
The interaction of the central mitotic checkpoint component BUB1 with the mitotic kinetochore protein Blinkin is required for the kinetochore localization and function of BUB1 in the mitotic spindle assembly checkpoint, the regulatory mechanism of the cell cycle that ensures the even distribution of chromosomes during the transition from metaphase to anaphase. Here, we report the 1.74 Å resolution...
About 10% of all protein kinases are predicted to be enzymatically inactive pseudokinases, but the structural details of kinase inactivation have remained unclear. We present the first structure of a pseudokinase, VRK3, and that of its closest active relative, VRK2. Profound changes to the active site region underlie the loss of catalytic activity, and VRK3 cannot bind ATP because of residue substitutions...
Several virulent bacteria have the ability to manipulate the host cell actin cytoskeleton as part of their pathogenic strategy. These pathogens subvert the host cell actin polymerization machinery for various purposes including motility within host cells, cell-to-cell spread, and to prevent phagocytic engulfment by professional phagocytes. In contrast to intracellular pathogens, pathogenic Escherichia...
Protein domains are compact evolutionary units of structure and function that usually combine in proteins to produce complex domain arrangements. In order to study their evolution, we reconstructed genome-based phylogenetic trees of architectures from a census of domain structure and organization conducted at protein fold and fold-superfamily levels in hundreds of fully sequenced genomes. These trees...
IL-7 and IL-7Rα bind the γ c receptor, forming a complex crucial to several signaling cascades leading to the development and homeostasis of T and B cells. We report that the IL-7Rα ectodomain uses glycosylation to modulate its binding constants to IL-7, unlike the other receptors in the γ c family. IL-7 binds glycosylated IL-7Rα 300-fold more tightly than unglycosylated IL-7Rα, and...
In this issue, Liu et al. (2009) used NMR to provide the most complete information to date on the structure of Arf1 and the role of myristate in GDP/GTP exchange. Unanticipated details lead to speculation about functions for the N and C termini of Arfs.
Extended all-atom molecular dynamics simulations on all protein metafolds have been performed to obtain a complete picture of the gas phase proteome. The structural atlas of the gas phase proteome obtained here shows an unexpected maintenance of the global and local structure and of the general deformability pattern upon transfer to the gas phase under electrospray conditions. Despite a general compression,...
The COP9 signalosome (CSN) is an eight-subunit protein complex that is found in all eukaryotes. Accumulating evidence indicates its diverse biological functions that are often linked to ubiquitin-mediated proteolysis. Here we applied an emerging mass spectrometry approach to gain insight into the structure of the CSN complex. Our results indicate that the catalytically active human complex, reconstituted...
Small GTPase Rab6 regulates vesicle trafficking at the level of Golgi via recruitment of numerous and unrelated effectors. The crystal structure of Rab6a(GTP) in complex with a 378-residue internal fragment of the effector Rab6IP1 was solved at 3.2 Å resolution. This Rab6IP1 region encompasses an all α-helical RUN domain followed in tandem by a PLAT domain that adopts a β sandwich fold. The structure...
The Ras-specific nucleotide exchange factor Son of sevenless (Sos) is inactive without Ras bound to a distal allosteric site. In contrast, the catalytic domain of Ras guanine nucleotide releasing factor 1 (RasGRF1) is active intrinsically. By substituting residues from RasGRF1 into Sos, we have generated mutants of Sos with basal activity, partially relieved of their dependence on allosteric activation...
The ROP2 protein and its paralogs are important virulence factors secreted into the host cell by the parasite Toxoplasma gondii. Here we describe the crystal structure of a large and soluble domain of mature ROP2, representative of the ROP2-like protein family. This is a structure of a protein-kinase fold that is devoid of catalytic residues and does not bind ATP. Various structural extensions constitute...
MAP2Ks are dual-specificity protein kinases functioning at the center of three-tiered MAP kinase modules. The structure of the kinase domain of the MAP2K MEK6 with phosphorylation site mimetic aspartic acid mutations (MEK6/ΔN/DD) has been solved at 2.3 Å resolution. The structure reveals an autoinhibited elongated ellipsoidal dimer. The enzyme adopts an inactive conformation, based upon structural...
The formation of stable 18S U11/U12 di-snRNPs before their association with the pre-mRNA is a characteristic feature of the minor spliceosome. During the spliceosomal assembly, the 18S snRNP binds cooperatively to the introns' 5′ splice and branch point site. The molecular basis for this recognition is still unknown. Here, we report the solution structure of the U11-48K CHHC Zn finger, a domain unique...
The minichromosome maintenance (MCM) proteins, members of the AAA+ (ATPase associated with diverse cellular activities) superfamily, are believed to constitute the replicative helicase in eukaryotic and archaeal species. Here, we present the 1.9 Å resolution crystal structure of a monomeric MCM homolog from Methanopyrus kandleri, the first crystallographic structure of a full-length MCM. We also present...
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