Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0235108 (tense)
 2,176 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The binding of nucleotides to nucleoside-diphosphate kinase from pig heart was studied using the dye rose Bengal as an optical probe. By difference absorption spectroscopy and by equilibrium dialysis it was shown that one dye molecule strongly bound per enzyme subunit. By competition with nucleotides it was shown that two nucleotide-binding sites exist on each subunit of either unphosphorylated or phosphorylated enzyme: one of them binds ATP or ADP tightly, the other one binds rose Bengal tightly and ADP loosely. As detected by different affinities for rose Bengal the enzyme exists in two conformations: a 'relaxed' conformation induced by the binding of ADP, and a 'tense' conformation induced by the binding of ATP or by phosphorylation.
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PMID:Binding of nucleotides to nucleoside diphosphate kinase monitored by rose Bengal. 301 10

The direct evidence of dramatic conformational changes of the DnaB hexamer, induced by nucleotide binding, and the presence of multiple conformational states of the enzyme have been obtained by using analytical sedimentation equilibrium, sedimentation velocity studies, and the rigorous fluorescence titration technique. Equilibrium sedimentation measurements show that in the presence of the ATP nonhydrolyzable analog, AMP-PNP, the DnaB helicase fully preserves its hexameric structure. However, in the presence of the saturating concentration of AMP-PNP, the sedimentation coefficient of the hexamer is s20,w = 11.9 +/- 0.2 compared to the sedimentation coefficient s20,w = 10.5 +/- 0.2 of the free DnaB helicase hexamer. This large sedimentation coefficient change indicates dramatic global conformational transitions of the hexamer, encompassing all six subunits, upon binding the ATP analog. In the presence of ADP, the sedimentation coefficient is s20,w = 11.4 +/- 0.2, indicating that the conformation of the ADP form of the hexamer is different from the ATP form. The sedimentation coefficient of the ternary complex DnaB-(AMP-PNP)-depsilonA(pepsilonA)19, s20,w = 12.4, suggests that the DnaB helicase undergoes further conformational changes upon binding single-stranded DNA (ssDNA). The large global structural changes correlate with the functional activities of the enzyme. In the absence of the ATP analog, the hexamer exists in a "closed" conformation which has extremely low affinity toward ssDNA. Upon binding the ATP analog, the DnaB hexamer transforms into a "tense" state which binds ssDNA with an affinity of approximately 4 orders of magnitude higher than in the absence of the nucleotide. In the presence of ADP, the DnaB hexamer assumes a "relaxed" conformation. The functional difference between these two conformations is reflected in the much weaker allosteric effect of ADP on the ssDNA binding with the affinity constant approximately 3 orders of magnitude weaker than in the presence of the ATP analog (tense state).
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PMID:Global conformational transitions in Escherichia coli primary replicative helicase DnaB protein induced by ATP, ADP, and single-stranded DNA binding. Multiple conformational states of the helicase hexamer. 862 72

Microtubule-dependent motors of the kinesin family convert the energy from ATP hydrolysis into mechanical work in order to transport vesicles and organelles along microtubules. The motor domains of several kinesins have been solved by X-ray diffraction, but the conformational changes associated with force development remain unknown. Here we describe conformational properties of kinesin that might be related to the mechanism of action. First, we have evaluated the conformational variability among all known kinesin structures and find they are concentrated in six areas, most of which are functionally important either in microtubule binding or in linking the core motor to the stalk. Secondly, we show that there is an important difference between kinesins when compared with myosins or GTPases (with which kinesin motor domains bear structural and catalytic similarities); in the diphosphate-state (with bound ADP), all kinesins show a 'tight' nucleotide-binding pocket, comparable with myosin or GTPases in the triphosphate state, whose nucleotide-binding pockets become open, or 'loose', following nucleotide hydrolysis. Thus, kinesin-ADP appears to be in a tense state, resembling that observed in myosin-ATP or p21ras-GTP.
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PMID:Motor proteins of the kinesin family. Structures, variations, and nucleotide binding sites. 1023 57