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Journal Issue - Volume 3 Issue 1 (January 1994)

Abstract Heterotrimeric GTP‐binding proteins (G proteins) that are made up of α and βγy subunits couple many kinds of cell‐surface receptors to intracellular effector enzymes or ion channels. Every cell contains several types of receptors, G proteins, and effectors. The specificity with which G protein subunits interact with receptors and effectors defines the range of responses a cell is able to make to an external signal. Thus,...

Abstract The backbone dynamics of the immunoglobulin‐binding domain (Bl) of streptococcal protein G, uniformly labeled with 15N, have been investigated by two‐dimensional inverse detected heteronuclear 1H‐15N NMR spectroscopy at 500 and 600 MHz. 15N T1, T2, and nuclear Overhauser enhancement data were obtained for all 55 backbone NH vectors of the B1 domain at both field strengths. The overall correlation time obtained from an analysis of the T1/T2 ratios...

Abstract We have utilized Raman difference spectroscopy to investigate hydrogen bonding interactions of the guanine moiety in guanine nucleotides with the binding site of two G proteins, EF‐Tu (elongation factor Tu from Escherichia coli) and the c‐Harvey ras protein, p21 (the gene product of the human c‐H‐rus proto‐oncogene). Raman spectra of proteins complexed with GDP (guanosine 5′ diphosphate), IDP (inosine 5′ diphosphate), 6‐thio‐GDP, and...

Abstract A soluble form of the human interferon γ receptor that is required for the identification of interferonγantagonists was expressed in baculovirus‐infected insect cells. The protein carried N‐linked carbohydrate and showed a heterogeneity on denaturing polyacrylamide gels. We investigated the utilization of the potential sites for N‐linked glycosylation and the structure of the carbohydrate moieties of this soluble receptor....

Abstract The structures of two catalytically modified semisynthetic RNases obtained by replacing phenylalanine 120 with leucine and tyrosine have been determined and refined at a resolution of 2.0 Å (R = 0.161 and 0.184, respectively). These structures have been compared with the refined 1.8‐Å structure (R = 0.204) of the fully active phenylalanine‐containing enzyme (Martin PD, Doscher MS, Edwards BFP, 1987, J Biol Chem 262:15930‐15938) and...

Abstract NAD(P)H:quinone acceptor oxidoreductase (EC 1.6.99.2) (DT‐diaphorase) is a FAD‐containing reductase that catalyzes a unique 2‐electron reduction of quinones. It consists of 2 identical subunits. In this study, it was found that the carboxyl‐terminal portion of the 2 subunits can be cleaved by various proteases, whereas the amino‐terminal portion cannot. It was also found that proteolytic digestion of the enzyme can be...

Abstract The crystal structure of a membrane channel, homotrimeric porin from Rhodopseudomonas blastica has been determined at 2.0 Å resolution by multiple isomorphous replacement and structural refinement. The current model has an R‐factor of 16.5% and consists of 289 amino acids, 238 water molecules, and 3 detergent molecules per subunit. The partial protein sequence and subsequently the complete DNA sequence were determined. The general...

Abstract The crystal structure of unactivated ribulose 1, 5‐bisphosphate carboxylase/oxygenase from Nicotiana tabacum complexed with a transition state analog, 2‐carboxy‐D‐arabinitol 1, 5‐bisphosphate, was determined to 2.7 Å resolution by X‐ray crystallography. The transition state analog binds at the active site in an extended conformation. As compared to the binding of the same analog in the activated enzyme, the analog binds in...

Abstract The solution structure of the N‐terminal domain of the actin‐severing protein villin has been determined by multidimensional heteronuclear resonance spectroscopy. Villin is a member of a family of actin‐severing proteins that regulate the organization of actin in the eukaryotic cytoskeleton. Members of this family are built from 3 or 6 homologous repeats of a structural domain of approximately 130 amino acids that is...

Abstract The structure of Candida rugosa lipase in a new crystal form has been determined and refined at 2.1 Å resolution. The lipase molecule was found in an inactive conformation, with the active site shielded from the solvent by a part of the polypeptide chain — the flap. Comparison of this structure with the previously determined “open” form of this lipase, in which the active site is accessible to the solvent and presumably the...

Abstract In order to investigate the response of dynamic structure to removal of a disulfide bond, the dynamic structure of human lysozyme has been compared to its C77A/C95A mutant. The dynamic structures of the wild type and mutant are determined by normal mode refinement of 1.5‐Å‐resoltion X‐ray data. The C77AK95A mutant shows an increase in apparent fluctuations at most residues. However, most of the change originates from an...

Abstract The denaturation of Escherichia coli acyl carrier protein (ACP) in buffers containing both monovalent and divalent cations was followed by variable‐temperature NMR and differential scanning calorimetry. Both high concentrations of monovalent salts (Na+) and moderate concentrations of divalent salts (Ca2+) raise the denaturation temperature, but calorimetry indicates that a significant increase in the enthalpy of denaturation is...

Abstract The family of FMN‐dependent, α‐hydroxy acid‐oxidizing enzymes catalyzes substrate dehydrogenation by a mechanism the first step of which is abstraction of the substrate α‐proton (so‐called carbanion mechanism). For flavocytochrome b2 and lactate oxidase, it was shown that once on the enzyme this proton is lost only slowly to the solvent (Lederer F, 1984, In: Bray RC, Engel PC, Mayhew SG, eds, Flavins & flavoproteins, Berlin: Walter...

Abstract The 3‐dimensional structure of human carbonic anhydrase II (HCAII; EC 4.2.1.1) complexed with 3 structurally related inhibitors, la, lb, and lc, has been determined by X‐ray crystallographic methods. The 3 inhibitors (la = C8H12N2O4S3) vary only in the length of the substituent on the 4‐amino group: la, proton; lb, methyl; and lc, ethyl. The binding constants (Ki's) for la, Ib, and lc to HCAII are 1.52, 1.88, and 0.37 nM, respectively. These...

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