1H-NMR study of inter-segmental hydrogen bonds in sperm whale and horse apomyoglobins.

The research article involves a detailed Nuclear Magnetic Resonance (NMR) study on the sperm whale and horse apomyoglobins to understand the structural differences between apoproteins and holoproteins. The study specifically observes two hydrogen-bonded protons and concludes that the removal of heme causes a significant structural alteration in one interface but not in the other.

Introduction

• This study uses the NMR (Nuclear Magnetic Resonance) technique to investigate structural differences between apoproteins and holoproteins in sperm whale and horse apomyoglobins.
• Apoproteins are proteins lacking their necessary cofactor, while holoproteins are the non-covalent complex of an apoprotein and its respective cofactor—in this case, heme.
• In proteins, an essential aspect of their structure and function involves hydrogen bonding. This work focuses on two specific proton positions—HisB5 N(delta)H and HisEF5 N(epsilon)H—as these protons are involved in internal hydrogen bonds at certain interfaces of the protein structure.

Methodology and Results

• The researchers assigned and compared the NMR signals for the HisB5 N(delta)H and HisEF5 N(epsilon)H protons, with the signals from holoproteins, factoring in changes with pH and temperature.
• They note a marked difference in the line width of HisEF5 N(epsilon)H proton signals between the two protein forms, suggesting the removal of heme causes significant structural shifts in the EF-H interface.
• Conversely, for the HisB5 N(delta)H proton, the findings indicated no major structural changes in the B-GH interface.

Consistency with Past Research

• Their findings echo earlier research into the impact of removing heme from protein structures.
• Previous mutation and amide-proton-exchange kinetic studies suggest the A, B, G, and H helices of apomyoglobin maintain the same packing in the apoprotein form as they do in the holoprotein.
• Thus, the latest NMR findings provide fresh backing for preceding research while shedding light on the differing impacts of heme removal on various inter-segmental hydrogen bonds within these proteins.

While this NMR study focused on sperm whale and horse apomyoglobins, researchers may apply similar methodologies to a variety of proteins, potentially gaining new insights into how the presence or absence of cofactors shapes protein structure and function.