Design principles for chlorophyll-binding sites in helical proteins

Area of Science:

• Biochemistry and Molecular Biology
• Protein Engineering
• Bioinorganic Chemistry

Background:

• Cyclic tetrapyrroles like chlorophylls (Chl), bacteriochlorophylls (BChls), and hemes are vital biological catalysts.
• Designing de novo protein scaffolds for these cofactors is a key strategy for understanding functional diversity.
• Current efforts primarily focus on heme-binding proteins, leaving (B)Chl-binding less explored.

Purpose of the Study:

• To investigate the geometric parameters of (bacterio)chlorophyll [(B)Chl]-binding sites in natural protein structures.
• To determine factors influencing heme versus (B)Chl binding selectivity.
• To provide guidelines for designing specific heme- or (B)Chl-binding protein scaffolds.

Main Methods:

• Analysis of geometric parameters in a nonredundant set of natural (B)Chl protein structures.
• Comparison with a database of heme-binding helical histidines.
• Identification of consensus sequences for (B)Chl binding using computational and database approaches.

Main Results:

• A preference for the m-rotamer in helical histidines binding (B)Chls was observed, contrasting with the t-rotamer preference for heme-binding helical histidines.
• Rotamer type significantly influences cofactor positioning relative to the helix interface.
• Identified (B)Chl-binding consensus sequences differ from those for heme-binding proteins.

Conclusions:

• Histidine rotamer preference is a critical determinant for (B)Chl versus heme binding selectivity in helical protein sites.
• These findings offer valuable insights for constructing specific (B)Chl-binding protein templates.
• The study provides guidelines for computational optimization of designed protein scaffolds for (B)Chl binding.