P70 Crystallization of the HbI–pCys protein complex from Lucina pectinata both in excess and absence of H2S

Abstract

Background Understanding the interactions between hydrogen sulfide (H2S) and proteins offers great insight into different aspect of human health. Curiously enough there is a wide variety of organisms that strive in concentrations of 2–5 mM of H2S and even more, were we humans would perish. One organism that lives under this condition is Lucina pectina, a bivalve that contains three hemoglobins and one of them, hemoglobin I (HbI), is capable of transporting H2S. Furthermore, HbI is intimately associated to a protein rich in cysteine (pCys) with unknown structure and function. This two proteins form a complex that may be responsible for the transfer and storage of H2S. Therefore, to understand possible changes in protein–protein interaction as a result of the H2S presence may shed light into many questions revolving around the delicate balance of H2S concentration and protein structures. Methods To resolve the three-dimensional structure of this protein complex, we study the protein–protein interaction through X-ray crystallography both in excess and absence of H2S. Unfortunately the crystallographic structure determination of proteins is limited by the ability to obtain protein crystals. Thus the bottleneck step for protein structure determination is achieving crystals that can diffract to atomic resolution (higher than 3A). Crystals of micrometers have been obtained by preliminary experiments using the HbI–pCys protein complex and the hanging drop technique. To optimize the crystal quality, experiments are being conducted using a counter diffusion gel crystallization approach. Results Preliminary experiments testing different crystallization conditions on the HbI–pCys protein complex (in the absence of H2S) gave small crystal hits for ammonium sulfate (in various buffers) and potassium, sodium- tartrate as precipitant salts. Conclusion The condition to grow HbI–pCys crystals were appropriate but must be improved.