Structural mapping of an aggregation nucleation site in a molten globule intermediate

Protein aggregation plays an important role in biotechnology and also cause s numerous diseases. Human carbonic anhydrase II is a suitable model protei n for studying the mechanism of aggregation. We found that a molten globule state of the enzyme formed aggregates. The intermolecular interactions inv olved in aggregate formation were localized in a direct way by measuring ex cimer formation between each of 20 site-specific pyrene-labeled cysteine mu tants. The contact area of the aggregated protein was very specific, and al l sites included in the intermolecular interactions were located in the lar ge beta-sheet of the protein, within a limited region between the central b eta-strands 4 and 7. This substructure is very hydrophobic, which underline s the importance of hydrophobic interactions between specific beta-sheet co ntaining regions in aggregate formation.