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Chiral checkpoints during protein biosynthesis.

Santosh Kumar Kuncha1,2, Shobha P Kruparani1, Rajan Sankaranarayanan3

  • 1Council of Scientific and Industrial Research (CSIR)-Centre for Cellular and Molecular Biology (CCMB), Hyderabad, Telangana 500007, India.

The Journal of Biological Chemistry
|October 9, 2019
PubMed
Summary

Cells maintain protein homochirality using "chiral checkpoints" like aminoacyl-tRNA synthetases (aaRSs) and the ribosome to exclude d-amino acids. D-aminoacyl-tRNA deacylase (DTD) acts as a proofreader, ensuring translation fidelity.

Keywords:
D-amino acidsamino acidaminoacyl tRNA synthetasecheckpoint controlchiralitygenetic codeproofreadingproteinsribosomestereoselectivitytransfer RNA (tRNA)translationtranslation elongation factor

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Cell Biology

Background:

  • Proteins are typically composed solely of l-amino acids, a property known as homochirality, essential for proper folding and cellular function.
  • While the roles of d-amino acids in bacterial cell walls and neurotransmission are known, their broader physiological significance is a recent discovery.
  • Maintaining enantiomeric purity during protein synthesis is crucial for cellular processes.

Purpose of the Study:

  • To review the occurrence and physiological roles of d-amino acids.
  • To explore the molecular mechanisms, termed "chiral checkpoints," that ensure enantiomeric fidelity during protein translation.
  • To discuss the potential applications of d-amino acids in synthetic biology.

Main Methods:

  • Review of existing literature on d-amino acid occurrence, roles, and mechanisms of exclusion during translation.
  • Analysis of the functions of key factors involved in maintaining chiral fidelity: aminoacyl-tRNA synthetases (aaRSs), elongation factor thermo-unstable (EF-Tu), the ribosome, and d-aminoacyl-tRNA deacylase (DTD).
  • Discussion of the implications of these mechanisms for protein synthesis and potential synthetic biology applications.

Main Results:

  • Cells possess sophisticated systems to prevent the incorporation of d-amino acids into nascent polypeptide chains.
  • Aminoacyl-tRNA synthetases (aaRSs), EF-Tu, and the ribosome function as "chiral checkpoints" that preferentially select l-aminoacyl-tRNAs.
  • D-aminoacyl-tRNA deacylase (DTD) acts as a "chiral proofreader" by removing misincorporated d-amino acids from tRNAs, a conserved mechanism across all life forms.

Conclusions:

  • Enantiomeric fidelity is a critical aspect of translation, safeguarded by multiple molecular mechanisms.
  • The identified "chiral checkpoints" and proofreading systems are essential for maintaining cellular function and preventing the deleterious effects of incorrect amino acid stereoisomers.
  • Understanding these mechanisms opens avenues for exploring the use of d-amino acids in synthetic biology.