Crystal Structure Of Ca2 Research Articles

Critical Hydrophobic Interactions between Phosphorylation and Actuator Domains of Ca2+-ATPase for Hydrolysis of Phosphorylated Intermediate

Functional roles of seven hydrophobic residues on the interface between the actuator (A) and phosphorylation (P) domains of sarcoplasmic reticulum Ca2+-ATPase were explored by alanine and serine substitutions. The residues examined were Ile179/Leu180/Ile232 on the A domain, Val705/Val726 on the P domain, and Leu119/Tyr122 on the loop linking the A domain and M2 (the second transmembrane helix). These residues gather to form a hydrophobic cluster around Tyr122 in the crystal structures of Ca2+-ATPase in Ca2+-unbound E2 (unphosphorylated) and E2P (phosphorylated) states but are far apart in those of Ca2+-bound E1 (unphosphorylated) and E1P (phosphorylated) states. The substitution-effects were also compared with those of Ile235 on the A domain/M3 linker and those of T181GE of the A domain, since they are in the immediate vicinity of the Tyr122-cluster. All these substitutions almost completely inhibited ATPase activity without inhibiting Ca2+-activated E1P formation from ATP. Substitutions of Ile235 and T181GE blocked the E1P to E2P transition, whereas those in the Tyr122-cluster blocked the subsequent E2P hydrolysis. Substitutions of Ile235 and Glu183 also blocked EP hydrolysis. Results indicate that the Tyr122-cluster is formed during the E1P to E2P transition to configure the catalytic site and position Glu183 properly for hydrolyzing the acylphosphate. Ile235 on the A domain/M3 linker likely forms hydrophobic interactions with the A domain and thereby allowing the strain of this linker to be utilized for large motions of the A domain during these processes. The Tyr122-cluster, Ile235, and T181GE thus seem to have different roles and are critical in the successive events in processing phosphorylated intermediates to transport Ca2+.

Phosphoryl transfer and calcium ion occlusion in the calcium pump.

A tight coupling between adenosine triphosphate (ATP) hydrolysis and vectorial ion transport has to be maintained by ATP-consuming ion pumps. We report two crystal structures of Ca2+-bound sarco(endo)plasmic reticulum Ca2+-adenosine triphosphatase (SERCA) at 2.6 and 2.9 angstrom resolution in complex with (i) a nonhydrolyzable ATP analog [adenosine (beta-gamma methylene)-triphosphate] and (ii) adenosine diphosphate plus aluminum fluoride. SERCA reacts with ATP by an associative mechanism mediated by two Mg2+ ions to form an aspartyl-phosphorylated intermediate state (Ca2-E1 approximately P). The conformational changes that accompany the reaction with ATP pull the transmembrane helices 1 and 2 and close a cytosolic entrance for Ca2+, thereby preventing backflow before Ca2+ is released on the other side of the membrane.

A Contribution to the Stereochemistry of Earth Alkaline Selenites: Synthesis and Crystal Structure of Ca2(SeO3)(Se2O5), Ba(SeO3), and Ba(Se2O5)

The compounds Ca2(SeO3)(Se2O5), Ba(SeO3), and Ba(Se2O5) were obtained at low-hydrothermal conditions from aqueous solutions of SeO2 by reaction with the respective earth alkaline carbonate. The crystal structures were determined by direct methods from single crystal X-ray diffraction data. Ca2(SeO3)(Se2O5): space group P*, Z=2, a=5.517(1), b=8.210(2), c=8.716(2) A, α=92.47(2), β=95.92(2), γ=97.15(2)°, V=389.0(2) A3, R 1=0.017; Ba(SeO3): space group P21/m, Z=2, a=4.677(2), b=5.645(2), c=6.851(3) A, β=107.16(2)°, V=172.8(1) A3, R 1=0.022, Ba(Se2O5): space group P21/c, Z=4, a=4.553(1), b=11.724(3), c=9.758(2) A, β=92.66(2)°, V=520.3(2)A3, R1=0.027. All three compounds have framework structures; in the case of Ca2(SeO3)(Se2O5), subunits of edge-sharing CaO n polyhedra forming sheets parallel to (010) can be emphasized. Ba(SeO3) belongs to the structure type of KClO3. In Ba(Se2O5), chains of face-sharing BaO9 polyhedra along [100] are present. The calcium atoms are 7- and 8-coordinated with mean Ca–O bond lengths of 2.42 and 2.48 A, the barium atoms have nine oxygen ligands with mean Ba–O bond lengths of 2.87 A.

A Peptide Model for Calmodulin Trapping by Calcium/Calmodulin-dependent Protein Kinase II

Autophosphorylation of Ca2+/calmodulin-dependent protein kinase II (CaM-kinase) induces a more than 1000-fold increase in calmodulin (CaM)-binding affinity by dramatically decreasing the off-rate for CaM. In this report, we investigate the molecular mechanism for this phenomenon by comparing the rate of dissociation of a novel fluorescently labeled CaM from two synthetic peptides and from the phosphorylated and nonphosphorylated forms of a recombinant preparation of CaM-kinase. Dissociation of a complex of CaM and CKII(296-312), a peptide representing close to the minimum CaM-binding domain of the alpha subunit of CaM-kinase, exhibited a fast off-rate of 5.0 s-1. This was similar to the off-rate of 1.1 s-1 for the dissociation of CaM from the nonphosphorylated form of CaM-kinase. In contrast, dissociation of CaM from either autophosphorylated CaM-kinase or peptide CKII(290-314) was extremely slow with apparent off-rates of about 3-9 x 10(-5) s-1. Along with information from the crystal structure of Ca2+/CaM bound to CKII(290-314) (Meador, W. E., Means, A. R., and Quiocho, F. A. (1993) Science 262, 1718-1721), our results suggest a model in which CaM-dependent autophosphorylation of CaM-kinase induces a conformational change in the region of the CaM-binding domain which allows the formation of additional stabilizing interactions with CaM. We predict that this involves amino acids 293-298 in CaM-kinase. The possible consequences of these observations on the reversibility of CaM trapping in native CaM-kinase are discussed.

Ca2[FeN2l und Sr2IFeN2]: Nitridoferrate(II) mit isolierten Anionen [Fe2N4]8- und [FeN2]4-/Ca2[FeN2] and Sr2[FeN2]: Nitridoferrates(II) with Isolated Anions [Fe2N4]8- and [FeN2]4-

Ca2[FeN2] (monocl., C2/m (No. 12); a = 1093.0(2) pm, b = 496.0(1) pm, c = 684.4(1) pm, β = 121.09(1)°; Z = 4) and Sr2[FeN2] (tricl., P1̄ (No. 2); a = 653.8(1) pm, b = 869.0(2) pm, c = 893.2(2) pm, α = 90.22(2)°, β = 109.45(1)°, γ = 102.30(1)°; Z = 5) were prepared by reaction of mixtures Ca3N2/Fe (Sr2N/Fe) with nitrogen (1 atm) at 850 C. The crystal structure of Ca2[FeN2] contains isolated planar anions [Fe2N4]8-; in the crystal structure of Sr2[FeN2] planar [Fe2N4]8- units are present as well as linear anions [FeN2]4-.