Structure of arthropodan hemocyanin

Area of Science:

• Biochemistry
• Structural Biology
• X-ray Crystallography

Background:

• Hemocyanins are copper-containing proteins responsible for oxygen transport in many invertebrates.
• Type III copper proteins, like hemocyanins, feature a unique dinuclear copper active site crucial for oxygen binding.
• Understanding hemocyanin structure provides insights into respiratory pigment evolution and function.

Purpose of the Study:

• To determine the high-resolution X-ray structure of spiny lobster deoxy-hemocyanin.
• To elucidate the structural organization of the hemocyanin hexamer and its subunits.
• To characterize the location and coordination of the oxygen-binding copper site.

Main Methods:

• X-ray crystallography was employed to determine the structure at 3.2 Å resolution.
• The molecular weight and quaternary structure were analyzed.
• The arrangement of protein domains and the copper-binding site were examined.

Main Results:

• The X-ray structure of spiny lobster deoxy-hemocyanin was resolved.
• The protein is a hexamer (approximately 460,000 MW) with subunits comprising three domains.
• The dinuclear copper site, coordinated by three histidines per copper, resides in the second domain.
• The hexamer exhibits a trimer-of-dimers quaternary structure.
• Structural features suggest a conserved architecture across arthropodan hemocyanins.

Conclusions:

• The study provides a detailed structural model of spiny lobster deoxy-hemocyanin.
• The findings reveal the organization of the oxygen-binding site and the hexamer assembly.
• The conserved polypeptide architecture implies a common evolutionary origin for arthropodan hemocyanins.