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Journal Issue - Volume 8 Issue 3 (1999)

Abstract We have determined the three‐dimensional solution structure of the complex of Lactobacillus casei dihydrofolate reductase and the anticancer drug trimetrexate. Two thousand seventy distance, 345 dihedral angle, and 144 hydrogen bond restraints were obtained from analysis of multidimensional NMR spectra recorded for complexes containing 15N‐labeled protein. Simulated annealing calculations produced a family of 22 structures fully consistent with...

Abstract The high affinity interleukin‐2 receptor is composed of three cell surface subunits, IL‐2Rα, IL‐2Rβ, and IL‐2Rγ. Functional forms of the IL‐2 receptor exist, however, that enlist only two of the three subunits. On activated T‐cells, the α‐ and β‐subunits combine as a preformed heterodimer (the pseudo‐high affinity receptor) that serves to capture IL‐2. On a subpopulation of natural killer cells, the β‐ and γ‐subunits...

Abstract The heme‐containing catalase HPII of Escherichia coli consists of a homotetramer in which each subunit contains a core region with the highly conserved catalase tertiary structure, to which are appended N‐ and C‐terminal extensions making it the largest known catalase. HPII does not bind NADPH, a cofactor often found in catalases. In HPII, residues 585–590 of the C‐terminal extension protrude into the pocket corresponding to ...

Abstract This paper reports on an insulin analogue with 12.5‐fold receptor affinity, the highest increase observed for a single replacement, and on its solution structure, determined by NMR spectroscopy. The analogue is [D‐AlaB26]des‐(B27‐B30)‐tetrapeptide‐insulin‐B26‐amide. C‐terminal truncation of the B‐chain by four (or five) residues is known not to affect the functional properties of insulin, provided the...

Abstract The most common form of systemic amyloidosis originates from antibody light chains. The large number of amino acid variations that distinguish amyloidogenic from nonamyloidogenic light chain proteins has impeded our understanding of the structural basis of light‐chain fibril formation. Moreover, even among the subset of human light chains that are amyloidogenic, many primary structure differences are found. We compared the...

Abstract CyclicAMP receptor protein (CRP) regulates transcription of numerous genes in Escherichia coli. Both cAMP and cGMP bind CRP, but only cAMP induces conformational changes that dramatically increase the specific DNA binding activity of the protein. We have shown previously that our protein footprinting technique is sensitive enough to detect conformational changes in CRP by cAMP [Baichoo N, Heyduk T. 1997. Biochemistry 36:10830–10836]....

Abstract δ‐Crystallin, the major soluble protein component of the avian and reptilian eye lens, is homologous to the urea cycle enzyme argininosuccinate lyase (ASL). In duck lenses there are two δ crystallins, denoted δ1 and δ2. Duck δ2 is both a major structural protein of the lens and also the duck orthologue of ASL, an example of gene recruitment. Although 94% identical to δ2/ASL in the amino acid sequence, δ1 is enzymatically...

Abstract Thymidylate synthase (TS) converts dUMP to dTMP by reductive methylation, where 5,10‐methylenetetrahydrofolate is the source of both the methylene group and reducing equivalents. The mechanism of this reaction has been extensively studied, mainly using the enzyme from Escherichia coli. Bacillus subtilis contains two genes for TSs, ThyA and ThyB. The ThyB enzyme is very similar to other bacterial TSs, but the ThyA enzyme is ...

Abstract The heat stable inhibitor of cAMP‐dependent protein kinase (PKIα) contains both a nuclear export signal (NES) and a high affinity inhibitory region that is essential for inhibition of the catalytic subunit of the kinase. These functions are sequentially independent. Two‐dimensional NMR spectroscopy was performed on uniformly [15N]‐labeled PKIα to examine its structure free in solution. Seventy out of 75 residues were identified, and...

Abstract The energetics of structural changes in the holo and apo forms of α‐lactalbumin and the transition between their native and denatured states induced by binding Ca2+ and Na+ have been studied by differential scanning and isothermal titration microcalorimetry and circular dichroism spectroscopy under various solvent conditions. Removal of Ca2+ from the protein enhances its sensitivity to pH and ionic conditions due to noncompensated...

Abstract To explore the structure of the pore‐forming fragment of colicin E1 in membranes, a series of 23 consecutive single cysteine substitution mutants was prepared in the sequence 402–424. Each mutant was reacted with a sulfhydryl‐specific reagent to generate a nitroxide labeled side chain, and the mobility of the side chain and its accessibility to collision with paramagnetic reagents was determined from the electron...

Abstract An α‐helix and a β‐strand are said to be interactively packed if at least one residue in each of the secondary structural elements loses 10% of its solvent accessible contact area on association with the other secondary structural element.An analysis of all such 5,975 nonidentical α/β units in protein structures, defined at 2.5Å resolution, shows that the interaxial distance between the α‐helix and theβ‐strand is linearly...

Abstract Left‐handed polyproline II helices (PPII) are contiguous elements of protein secondary structure in which the ø and Ψ angles of constituent residues are restricted to around –75° and 145°, respectively. They are important in structural proteins, in unfolded states and as ligands for signaling proteins. Here, we present a survey of 274 nonhomologous polypeptide chains from proteins of known structure for regions that form...

Abstract Glucosamine 6‐phosphate synthase converts fructose‐6P into glucosamine‐6P or glucose‐6P depending on the presence or absence of glutamine. The isomerase activity is associated with a 40‐kDa C‐terminal domain, which has already been characterized crystallographically. Now the three‐dimensional structures of the complexes with the reaction product glucose‐6P and with the transition state analog 2‐amino‐2‐deoxyglucitol‐6P have...

Abstract The protein‐protein interaction energy of 12 nonhomologous serine protease‐inhibitor and 15 antibody‐antigen complexes is calculated using a molecular mechanics formalism and dissected in terms of the main‐chain vs. side‐chain contribution, nonrotameric side‐chain contributions, and amino acid residue type involvement in the interface interaction. There are major differences in the interactions of the...

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