Pseudosymmetry in the structure of myohemerythrin

Area of Science:

• Structural biology
• Biophysics
• Protein science

Background:

• Myohemerythrin is a protein found in sipunculan worms, essential for oxygen transport.
• Understanding protein structure is key to elucidating protein function and evolution.

Purpose of the Study:

• To investigate the three-dimensional structure of myohemerythrin from Themiste zostericola.
• To identify approximate symmetry operators within the myohemerythrin molecule.
• To explore potential evolutionary relationships indicated by structural and sequence homologies.

Main Methods:

• Analysis of electron density distribution at 5.5 Å resolution.
• Refinement of a local 2-fold axis using least squares.
• Rotation function analysis of the Patterson function to identify rotational symmetry.
• Inspection of amino acid sequence for repeated structural elements.

Main Results:

• A local 2-fold axis was identified, relating the A-B and C-D helix pairs with a correlation coefficient of 0.56.
• Rotation function analysis confirmed the 2-fold symmetry and revealed approximate D4 point group symmetry.
• A 28% amino acid identity was found between the A-B and C-D helix pairs, suggesting significant homology.

Conclusions:

• Myohemerythrin possesses significant internal approximate symmetry.
• The observed sequence homology, though low, is considered significant and indicative of evolutionary relationships.
• These findings contribute to understanding protein structure-function dynamics and evolutionary history.