BackgroundSteroidogenic acute regulatory (StAR) protein related lipid transfer (START) domains are small globular modules that form a cavity where lipids and lipid hormones bind. These domains can transport ligands to facilitate lipid exchange between biological membranes, and they have been postulated to modulate the activity of other domains of the protein in response to ligand binding. More than a dozen human genes encode START domains, and several of them are implicated in a disease.Principal FindingsWe report crystal structures of the human STARD1, STARD5, STARD13 and STARD14 lipid transfer domains. These represent four of the six functional classes of START domains.SignificanceSequence alignments based on these and previously reported crystal structures define the structural determinants of human START domains, both those related to structural framework and those involved in ligand specificity.Enhanced version This article can also be viewed as an enhanced version in which the text of the article is integrated with interactive 3D representations and animated transitions. Please note that a web plugin is required to access this enhanced functionality. Instructions for the installation and use of the web plugin are available in Text S1.
Altered inositol metabolism is implicated in a number of diabetic complications. The first committed step in mammalian inositol catabolism is performed by myo-inositol oxygenase (MIOX), which catalyzes a unique four-electron dioxygen-dependent ring cleavage of myo-inositol to D-glucuronate. Here, we present the crystal structure of human MIOX in complex with myo-inosose-1 bound in a terminal mode to the MIOX diiron cluster site. Furthermore, from biochemical and biophysical results from N-terminal deletion mutagenesis we show that the N terminus is important, through coordination of a set of loops covering the active site, in shielding the active site during catalysis. EPR spectroscopy of the unliganded enzyme displays a two-component spectrum that we can relate to an open and a closed active site conformation. Furthermore, based on site-directed mutagenesis in combination with biochemical and biophysical data, we propose a novel role for Lys 127 in governing access to the diiron cluster.myo-Inositol is a cyclitol that plays a crucial role in all eukaryotic cells by serving as a backbone for the most important second messengers: inositol phosphates and their lipid derivatives, phosphoinositides. Although inositol phosphates and phosphoinositides have been and continue to be the focus of intense study, the mechanisms for maintenance of total cellular inositol levels and the medical implications of deranged intracellular inositol levels are less studied. It is known that inositol homeostasis is often disturbed in diabetes (1) and that intracellular depletion of myo-inositol is associated with common diabetic complications, such as cataracts, nephropathies, retinopathies, and neuropathies (2). In mammalian cells, the only pathway for inositol breakdown utilizes myo-inositol oxygenase (MIOX) 3 to catalyze the first committed step by a dioxygen-dependent cleavage between C1 and C6 of the inositol ring to form D-glucuronate, which can then enter the glucuronate-xylulose pathway (2). Therapeutic intervention aimed at inhibiting MIOX activity may be a future cure for diabetic complications caused by inositol depletion.18 O labeling studies have shown that MIOX incorporates only a single oxygen into the product and that oxygen is found exclusively in the D-glucuronate carboxylate group. MIOX has a pH optimum of 9.5 (3) with myo-inositol (K m ϭ 5.9 mM; k cat ϭ 11 min Ϫ1 (2)) and its epimer D-chiroinositol (K m ϭ 33 mM; k cat ϭ 2.3 min Ϫ1 (2)) as its only known substrates. Moreover, the only known reasonably potent inhibitor is myo-inosose-1 (K i ϭ 62 M (3)). It has been noted that an N-terminally truncated fragment starting at Thr 32 is formed upon storage of recombinant protein (4). Interestingly, this uncharacterized N-terminal fragment is also observed in vivo (5).It was recently shown, using EPR and Mössbauer spectroscopy, that MIOX is a new member of the nonheme diiron-dependent dioxygen-activating family (6). Interestingly, the sequence indicated strong dissimilarity to other members of this family (6) that all fe...
Phosphatases are a diverse group of enzymes that regulate numerous cellular processes. Much of what is known relates to the tyrosine, threonine, and serine phosphatases, whereas the histidine phosphatases have not been studied as much. The structure of phosphohistidine phosphatase (PHPT1), the first identified eukaryotic-protein histidine phosphatase, has been determined to a resolution of 1.9 Å using multiple-wavelength anomalous dispersion methods. This enzyme can dephosphorylate a variety of proteins (e.g. ATP-citrate lyase and the -subunit of G proteins). A putative active site has been identified by its electrostatic character, ion binding, and conserved protein residues. Histidine 53 is proposed to play a major role in histidine dephosphorylation based on these observations and previous mutational studies. Models of peptide binding are discussed to suggest possible mechanisms for substrate recognition.Reversible phosphorylation of residues is crucial in a variety of signaling pathways. Most of our understanding regarding these signaling events in eukaryotes comes from tyrosine, serine/threonine kinases, and phosphatases (1). Less well characterized is histidine phosphorylation-dependent signaling in eukaryotes. A little more than thirty years ago, Histone H4, the first vertebrate protein with a phosphorylated histidine residue, was identified (2). Since then there has been a measured increase in knowledge of mammalian histidine kinases (3). Unfortunately, very little information regarding eukaryotic histidine phosphatases has been available during this same period. This nescience is interesting because histidine phosphorylation is quite prevalent in the cell and likely accounts for ϳ6% of all phosphorylation in eukaryotes (4). Thus far, only one protein (the -subunit of heterotrimeric G proteins) in vertebrates has been identified as undergoing reversible histidine phosphorylation where both the kinase (NDPK B) and phosphatase (PHPT1) 2 are known (for a recent review, see Ref. 5). However, more information regarding histidine phosphatases is slowly beginning to emerge. To date, the only other structure of a histidine phosphatase is Escherichia coli SixA (6). Under certain anaerobic respiratory conditions, SixA is involved in down-regulation of the E. coli ArcB-to-ArcA phosphorelay system. SixA shows structural homology to the well studied family of arginine-histidine-glycine (RHG) phosphatases (6) but no sequence homology to PHPT1.Mammalian phosphohistidine phosphatase (PHPT1) was first identified and characterized as a 14-kDa protein in 2002 (7,8). The enzyme can dephosphorylate the phosphohistidinecontaining peptide succinyl-Ala-His(P)-Pro-Phe-p-nitroanilide, E. coli cheA, rabbit ATP-citrase lyase, and the rat -subunit of G proteins (7-10). PHPT1 has been suggested to be highly involved in neuronal function. Unlike most phosphatases it does not require divalent cations for activity. Individual point mutations of conserved histidine and arginine residues determined that Arg 45 , His 53 , and His 102 ma...
Perturbed cell adhesion mechanisms are crucial for tumor invasion and metastasis. A cell adhesion protein, TSLC1 (tumor suppressor in lung cancer 1), is inactivated in a majority of metastatic cancers. DAL-1 (differentially expressed in adenocarcinoma of the lung protein), another tumor suppressor, binds through its FERM domain to the TSLC1 C-terminal, 4.1 glycophorin C-like, cytoplasmic domain. However, the molecular basis for this interaction is unknown. Here, we describe the crystal structure of a complex between the DAL-1 FERM domain and a portion of the TSLC1 cytoplasmic domain. DAL-1 binds to TSLC1 through conserved residues in a well defined hydrophobic pocket in the structural C-lobe of the DAL-1 FERM domain. From the crystal structure, it is apparent that Tyr 406 and Thr 408 in the TSLC1 cytoplasmic domain form the most important interactions with DAL-1, and this was also confirmed by surface plasmon resonance studies. Our results refute earlier exon deletion experiments that indicated that glycophorin C interacts with the ␣-lobe of 4.1 FERM domains.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.