Solution Structure of Human β-Parvalbumin and Structural Comparison with Its Paralog α-Parvalbumin and with Their Rat Orthologs^,

Abstract

The aim of this research was to determine the structure of human beta-parvalbumin (109 amino acids) and to compare it with its paralog and ortholog proteins. The structure was determined in solution using multinuclear and multidimensional NMR methods and refined using substitution of the EF-hand Ca(2+) ion with a paramagnetic lanthanide. The resulting family of structures had a backbone rmsd of 0.50 A. Comparison with rat oncomodulin (X-ray, 1.3 A resolution) as well as with human (NMR, backbone rmsd of 0.49 A) and rat (X-ray, 2.0 A resolution) parvalbumins reveals small but reliable local differences, often but not always related to amino acid variability. The analysis of these structures has led us to propose an explanation for the different affinity for Ca(2+) between alpha- and beta-parvalbumins and between parvalbumins and calmodulins.

Cytosolic Ca2+ Buffers

“…In both sites, the Ca 2þ ion in the center of the loop is coordinated by seven ligands sitting in the corners of a pentagonal bipyramid (Swain et al 1989). Results based on solution structures of a PV and b PV (Babini et al 2004) in the Ca 2þ -loaded and the apo (metal-free) form are summarized: (I) PV's Ca 2þ -loaded EF-hand domains and the linker region connecting the CD and EF domains are rather rigid structures; also the N-and C-termini of PV have a low intrinsic mobility (Baldellon et al 1998); (II) Differences in the structure of apo-and Ca 2þ -loaded forms of rat PV are small, mostly confined to the loop region. Thus, Ca 2þ binding does not require major structural rearrangements (Henzl and Tanner 2008); (III) The first two points also hold true for the Ca 2þ /Mg 2þ (EF) site in rat b PV, while the noncanonical CD site undergoes significant structural alterations, when Ca 2þ is removed from b PV (Henzl and Tanner 2007).…”

The continuing disappearance of “pure” Ca2+ buffers

“…1) [36]. While the crystal structure of PV was known early on [2], in the last few years, more structures of PV in solution from different species or b PV structures have been published [37]. They include NMR studies on C and N relaxation of the Ca 2+ -loaded pike and rat PV [18], the apo (metalfree form) of rat a PV [38] and b PV [39].…”

NMR Spectroscopy of Paramagnetic Metalloproteins

“…[119,130] When one of the two Ca 2 + ions is substituted with Tb 3 + , [119] many backbone signals (more than 50 %) are lost in the 1 H, 15 N-HSQC spectrum [131] because of 1 H Curie relaxation (Figure 11), while only 37 out of 109 signals are lost in the CACO spectrum.…”