Functionally Relevant Specific Packing Can Determine Protein Folding Routes

J Mol Biol. 2016 Jan 29;428(2 Pt B):509-21. doi: 10.1016/j.jmb.2015.12.014. Epub 2015 Dec 24.

Abstract

Functional residues can modulate the folding mechanisms of proteins. In some proteins, mutations to such residues can radically change the primary folding route. Is it possible then to learn more about the functional regions of a protein by investigating just its choice of folding route? The folding and the function of the protein Escherichia coli ribonuclease H (ecoRNase-H) have been extensively studied and its folding route is known to near-residue resolution. Here, we computationally study the folding of ecoRNase-H using molecular dynamics simulations of structure-based models of increasing complexity. The differences between a model that correctly predicts the experimentally determined folding route and a simpler model that does not can be attributed to a set of six aromatic residues clustered together in a region of the protein called CORE. This clustering, which we term "specific" packing, drives CORE to fold early and determines the folding route. Both the residues involved in specific packing and their packing are largely conserved across E. coli-like RNase-Hs from diverse species. Residue conservation is usually implicated in function. Here, the identified residues either are known to bind substrate in ecoRNase-H or pack against the substrate in the homologous human RNase-H where a substrate-bound crystal structure exists. Thus, the folding mechanism of ecoRNase-H is a byproduct of functional demands upon its sequence. Using our observations on specific packing, we suggest mutations to an engineered HIV RNase-H to make its function better. Our results show that understanding folding route choice in proteins can provide unexpected insights into their function.

Keywords: E. coli RNase-H; computational protein folding; energetic heterogeneity; folding mechanism; substrate binding.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Conserved Sequence
  • DNA Mutational Analysis
  • Escherichia coli / genetics
  • Escherichia coli / physiology*
  • Molecular Dynamics Simulation
  • Molecular Sequence Data
  • Mutant Proteins / chemistry
  • Mutant Proteins / genetics
  • Mutant Proteins / metabolism
  • Protein Conformation
  • Protein Folding*
  • Ribonuclease H / chemistry*
  • Ribonuclease H / genetics
  • Ribonuclease H / metabolism*

Substances

  • Mutant Proteins
  • Ribonuclease H
  • ribonuclease HI