Small-angle X-ray Scattering-based Three-dimensional Reconstruction of the Immunogen KLH1 Reveals Different Oxygen-dependent Conformations

Abstract

For decades the respiratory protein keyhole limpet hemocyanin (KLH1) from the marine gastropod Megathura crenulata has been used widely as a potent immunostimulant, useful hapten carrier, and valuable agent in the treatment of bladder carcinoma. Although much information on the immunological properties of KLH1 is available, biochemical and structural data are still incomplete. Small-angle x-ray scattering revealed the existence of two conformations, an oxy state being slightly more compact than the deoxy state. Based on small-angle scattering curves, a newly developed Monte Carlo algorithm delivered a surface representation of proteins. The massive changes of the surfaces of reconstructed didecameric KLH1 molecules are explained as a twist of the two non-covalently associated decameric half-molecules. Upon oxygenation, the KLH1 molecule becomes longer and skinnier. This study provides the first real evidence how a molluscan hemocyanin changes conformation during an allosteric transition.

Nautilus pompilius Hemocyanin: 9 Å Cryo-EM Structure and Molecular Model Reveal the Subunit Pathway and the Interfaces between the 70 Functional Units

“…As deduced from comparative SAXS analysis, oxygenation/deoxygenation of molluscan hemocyanins might conform to a massive conformational change of the cylinder surface that is explained by a twist along the 5-fold axis; 48 from these data it appears that upon oxygenation, the helical grooves become less pronounced (see Figure 2 of Hartmann et al 48 ). Therefore, it is possible that allosterism exists at two nested structural levels: strong interaction within the seven-site compartment proposed here as allosteric unit, and a weaker (and therefore hitherto overlooked) allosteric effect via the major and minor grooves, encompassing two or more of such prime allosteric units.…”

Similar enzyme activation and catalysis in hemocyanins and tyrosinases

“…Depending on the species decamers and didecamers are found (van Holde and Miller, 1995;Harris and Markl, 1999). The tertiary and quaternary structures of both mollusc and arthropod hemocyanin undergo large conformational transitions upon oxygenation, demonstrating a large flexibility in their structures (Hazes et al, 1993;Magnus et al, 1994;Cuff et al, 1998;Hartmann and Decker, 2002;Perbandt et al, 2003;Hartmann et al, 2004).…”

Crystallization and Preliminary Analysis of Crystals of the 24-Meric Hemocyanin of the Emperor Scorpion (Pandinus imperator)

“…It has been shown that these properties are associated with large conformational changes [19], [20],[21],[22],[23]. Among hemocyanins the four-hexamer hemocyanin of the emperor scorpion ( Pandinus imperator ) is known for its exceptionally high cooperativity with Hill coefficients (n H ) commonly ranging between 6–7 [24].…”