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D C Dalgarno

Publications and source records attributed to D C Dalgarno.

28 records · Page 2Linked to original sources
PubMed1984

1H-NMR studies of calmodulin. The nature of the Ca2+-dependent conformational change.

Using assignments of resonances in the 1H-NMR spectrum of calmodulin obtained by the use of large tryptic fragments of the molecule [Dalgarno, D. C., Klevit, R. E., Levine, B. A., Williams, R. J. P., Dobrowolski, Z., and Drabikowski, W. (1984) Eur. J. Biochem. 138, 281--289], the spectral changes which occur on Ca2+ binding to calmodulin have been examined in detail. Ca2+ binding occurs in two stages: the first two Ca2+ ions bind at sites III and IV (numbered from the N terminus) and the second two Ca2+ ions bind at sites I and II. The high-affinity binding causes perturbations of residues in both halves of the molecule, whereas binding at the two N-terminal sites only affects sidechains in that half of the molecule. The effects of binding Cd2+ to the Ca2+-binding sites of calmodulin have also been studied by 1H NMR. The cation induces spectral changes which are very similar to those seen for Ca2+, but some important differences do exist.

Binding Sites↗
PubMed1984

1H NMR studies of calmodulin. Resonance assignments by use of tryptic fragments.

Two tryptic fragments of the Ca2+ -binding protein calmodulin have been studied by high-resolution 1H NMR. TR1C (residues 1 - 77) spans the first two domains of the protein and TR2C (residues 78 - 148) spans the second two domains. The spectra indicate that each of the two-domain peptides assumes a conformation which is very close to that in the native protein. This characteristic holds both in the presence and in the absence of Ca2+ ions. Therefore, the resonance assignments obtained for the relatively simpler fragment spectra can be used to assign the spectrum of whole calmodulin. Analysis of the chemical shift patterns and nuclear Overhauser enhancement effects of several assigned resonances indicates that each half of calmodulin can be modelled after the two EF-hand Ca2+-binding proteins for which crystal structures are available, namely parvalbumin and intestinal Ca2+-binding protein.

Animals↗
PubMed1983

Proton-NMR studies of the solution conformations of vitamin-D-induced bovine intestinal calcium-binding protein.

1H NMR is used to study the solution structure of vitamin-D-induced bovine intestinal calcium-binding protein. The study of the native protein is aided by the recently published crystal structure; it is shown that the conformations of the molecule in the crystal and in solution are very similar. The effect of pH and temperature on the native structure is described. The structure of the apo protein is then described, and the effect of pH and temperature on its fold is outlined. A comparison between apo and native protein folds is made which indicates that the folds are very similar. The two folds are related by a calcium titration, which indicates that the protein binds two calcium ions sequentially. Both steps in the Ca2+ titration occur under conditions of slow exchange (kex 80 s-1). The effect of binding Ca2+ ions is to cause twisting motions of helices, with the helices acting as rods, relaying the conformational change induced by Ca2+ binding to the linker regions of the protein.

Animals↗
PubMed1983

The mobility of calcium-trigger proteins and its function.

Trigger activity implies the transfer of the energy of a signal to some amplified (energy) response. Actions in cells, from calcium concentration changes to major protein reorganization are discussed here. The changes must be fast, so mobile polymers must be involved. The first step is the calcium on/off binding to its receptor, calmodulin, troponin C or a comparable protein. Calcium binding is to a loop, EF-hand, between helices. The structures and internal mobilities of these proteins are described using nuclear magnetic resonance and the temperature dependence of NMR shifts. It is suggested that these proteins illustrate a general working hypothesis that proteins made from interacting helices as opposed to beta-sheet proteins will have relatively easy internal main chain motions. Loops connecting the helices then provide particularly obvious read-out points, for example of the initial message of calcium binding. These and other regions of loose structure appear to be associated with highly charged sequences. The further transfer of the trigger message is to highly mobile sequences in troponin I, troponin T and tropomyosin.

Amino Acid Sequence↗
PubMed1983

Structural information from NMR secondary chemical shifts of peptide alpha C-H protons in proteins.

The secondary chemical shift experienced by the 1H-NMR resonances of the alpha C-H protons in proteins can be correlated with their backbone torsional angles psi, which dictate the orientation of the alpha C-H proton to the adjacent carbonyl group. It is shown that alpha C-H protons present in beta-sheet regions experience downfield secondary shifts, whereas those in alpha-helix regions experience upfield secondary shifts. The predictive use of this correlation in assignment studies is illustrated for the calcium-binding protein paravalbumin, for which a crystal structure is available, and troponin C, for which no crystallographic data are available.

Amino Acid Sequence↗
PubMed1982

Identification of a surface actin-binding site on myosin.

The surface accessibility of mobile domains of rabbit fast muscle myosin subfragment-1 isoenzymes (subfragment-1(A1), (A2)) influenced by interaction with actin has been investigated by proton magnetic resonance spectroscopy using the soluble paramagnetic reagents Cr(CN)6(3-), Fe(CN)6(3-), Mn2+ and the Gd3+ salt of 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid as probes. Anionic probes interact principally with lysine residues disposed close to other non-charged sidechains in both isoenzymes. Additional resonances in subfragment-1(A1) not present in subfragment-1(A2) are also observed to be affected, notably the sharp signal at 3.23 ppm which derives from a -N+ (CH3)3 group found in the N-terminal segment of the A1 light chain, showing that this domain of interaction with actin (Prince et al. (1981) Eur. J. Biochem. 121, 213-219) is situated at a surface location. Different probes identify a heterogeneity in the location and function of mobile sidechains. These results suggest a configurational lability in the various parts of the myosin head, differentially constrained upon interaction with actin and consistent with a structure composed of relatively rigid domains linked by more flexible regions.

Actins↗