Delicate balance between functionally required flexibility and aggregation risk in a β-rich protein.
Susceptibility to aggregation is general to proteins because of the potential for intermolecular interactions between hydrophobic stretches in their amino acid sequences. Protein aggregation has been implicated in several catastrophic diseases, yet we still lack in-depth understanding about how proteins are channeled to this state. Using a predominantly β-sheet protein whose folding has been explored in detail, cellular retinoic acid-binding protein 1 (CRABP1), as a model, we have tackled the challenge of understanding the links between a protein's natural tendency to fold, 'breathe', and function with its propensity to misfold and aggregate. We identified near-native dynamic species that lead to aggregation and found that inherent structural fluctuations in the native protein, resulting in opening of the ligand-entry portal, expose hydrophobic residues on the most vulnerable aggregation-prone sequences in CRABP1. CRABP1 and related intracellullar lipid-binding proteins have not been reported to aggregate inside cells, and we speculate that the cellular concentration of their open, aggregation-prone conformations is sufficient for ligand binding but below the critical concentration for aggregation. Our finding provides an example of how nature fine-tunes a delicate balance between protein function, conformational variability, and aggregation vulnerability and implies that with the evolutionary requirement for proteins to fold and function, aggregation becomes an unavoidable but controllable risk.
Department of Biochemistry and Molecular Biology, ‡Program in Molecular and Cellular Biology, and §Department of Chemistry, University of Massachusetts , Amherst, Massachusetts 01003, United States.
Mylene C
MC
Ferrolino
Anastasia
A
Zhuravleva
Ivan L
IL
Budyak
Beena
B
Krishnan
Lila M
LM
Gierasch
D019943:Amino Acid Substitution; D000818:Animals; D041961:Deuterium Exchange Measurement; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D051379:Mice; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D011485:Protein Binding; D017510:Protein Folding; D055550:Protein Stability; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D058767:Protein Unfolding; D018168:Receptors, Retinoic Acid / Q000737:chemistry* / Q000235:genetics
D018168:Receptors, Retinoic Acid; C082927:retinoic acid binding protein I, cellular