Abstract
Beyond its role as an oxygen transport protein, the homodimer hemoglobin of blood clam Tegillarca granosa (Tg-HbI) has been found to possess antibacterial activity. However, the mechanism of antibacterial activity of Tg-HbI remain to be investigated. In this study, we investigated the effects of Cu2+ on the structure, peroxidase activity, and antibacterial ability of Tg-HbI. Tg-HbI was significantly inactivated by Cu2+ in a non-competitive inhibition manner, following first-order reaction kinetics. The Spectroscopy results showed that Cu2+ changed the iron porphyrin ring and the coordination of heme with proximal histidine of Tg-HbI, and increased the hydrophobicity of heme pocket. We found that proline could stabilize the heme pocket structure of Tg-HbI, hence, protect peroxidase activity and antimicrobial activity of Tg-HbI against damage by Cu2+. Our results suggest that Cu2+ inhibits the peroxidase and antibacterial activity of Tg-HbI by destroying its heme pocket structure and Tg-HbI probably plays an antibacterial role through its peroxidase activity. This result could provide insights into the antibacterial mechanism of Tg-HbI.
Highlights
The blood clam (Tegillarca granosa), a marine invertebrate of important economic value, inhabits the sandy muds of the intertidal zone in the east coast of China and Southeast Asia
The aim of the current work was to study the effects of Cu2+ on Tg-HbI with respect to changes in structure and antibacterial activity, which would be helpful in exploring the association of structure, peroxidase activity, and antibacterial activity, and could provide useful avenues for further research on the antibacterial mechanism of Tg-HbI
The enzyme activity gradually decreased in a time-dependent manner with first-order reaction kinetics, and inactivation of Tg-HbI accelerated with increase in Cu2+ concentration
Summary
The blood clam (Tegillarca granosa), a marine invertebrate of important economic value, inhabits the sandy muds of the intertidal zone in the east coast of China and Southeast Asia. T. granosa belongs to the family Arcidae of the class Bivalvia (phylum Mollusca), one of a few invertebrate groups that have hemoglobin-containing red hemocytes in the hemolymph (Bao et al, 2011a,b). Two kinds of hemoglobin (Hb), Tg-HbI (homodimer), and Tg-HbII (tetramer), have been purified from T. granosa hemocytes. Tg-HbI is made up of a single type of polypeptide chain, which differs from two chains of heterotetramer in molecular weight and isoelectric point (Bao et al, 2013, 2016; Wang et al, 2014). Homodimer Hb exists in only a few invertebrates (Weber and Vinogradov, 2001), unlike tetramer Hb, which exists in both vertebrates, and invertebrates.
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