Ca<Superscript>2+</Superscript> binding to complement-type repeat domains 5 and 6 from the low-density lipoprotein receptor-related protein

Background

The binding of ligands to clusters of complement-type repeat (CR)-domains in proteins of the low-density lipoprotein receptor (LDLR) family is dependent on Ca²⁺ ions. One reason for this cation requirement was identified from the crystal structure data for a CR-domain from the prototypic LDLR, which showed the burial of a Ca²⁺ ion as a necessity for correct folding and stabilization of this protein module. Additional Ca²⁺ binding data to other CR-domains from both LDLR and the LDLR-related protein (LRP) have suggested the presence of a conserved Ca²⁺ cage within CR-domains from this family of receptors that function in endocytosis and signalling.

Results

We have previously described the binding of several ligands to a fragment comprising the fifth and the sixth CR-domain (CR56) from LRP, as well as qualitatively described the binding of Ca²⁺ ions to this CR-domain pair. In the present study we have applied the rate dialysis method to measure the affinity for Ca²⁺, and show that CR56 binds 2 Ca²⁺ ions with an average affinity of K_D = 10.6 microM, and there is no indication of additional Ca²⁺ binding sites within this receptor fragment.

Conclusions

Both CR-domains of CR56 bind a single Ca²⁺ ion with an affinity of 10.6 microM within the range of affinities demonstrated for several other CR-domains.

     

Conformational flexibility of DNA

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Photoinduced hydrogen evolution in an artificial system containing photosystem I,hydrogenase,methyl viologen and mercaptoacetic acid

Hydrogen evolution was detected in an artificial system composed of light-harvesting unit of purified photosystem Ⅰ, catalyst ofhydrogenase, methyl viologen and electron donor under radiation. Absorption spectral features confirmed that electron transferfrom electron donors to proton was via a photoinduced reductive process of methyl viologen.2008 Dong Jin Qian. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.     

Schoenberg’s Theorem and Unitarily Invariant Random Arrays

Motivated by Schoenberg??s theorem in classical analysis and some recent work on the circular law, we extend the basic representations of unitarily invariant random arrays and functionals to the complex case. As in the real case, the basic building blocks are multiple Wiener?CIt? integrals on tensor products of a separable Hilbert space. The complex setting leads to some unexpected simplifications.     

Convergence of non-ergodic dynamical systems

Summary Let {T _t} be a flow on a probability space (S,L,}) which describes the time evolution of a dynamical system with state space S, and interpret as the initial distribution of the system. Then the distribution of the system at time t is given by T _t ^–1 . Our aim is to study the asymptotic behavior of T _t ^–1 both in general and in the particular cases of random rate and almost periodic systems. The results seem to indicate that convergence or mean convergence is the normal behavior in the non-ergodic case.