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Co‐evolution of multipartite interactions between an extended tmRNA tag and a robust Lon protease in Mycoplasma
Author(s) -
Ge Zhiyun,
Karzai A. Wali
Publication year - 2009
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2009.06923.x
Subject(s) - biology , protease , ribosome , rna , biochemistry , gene , enzyme
Summary Messenger RNAs that lack in‐frame stop codons promote ribosome stalling and accumulation of aberrant and potentially harmful polypeptides. The SmpB‐tmRNA quality control system has evolved to solve problems associated with non‐stop mRNAs, by rescuing stalled ribosomes and directing the addition of a peptide tag to the C‐termini of the associated proteins, marking them for proteolysis. In Escherichia coli , the ClpXP system is the major contributor to disposal of tmRNA‐tagged proteins. We have shown that the AAA+ Lon protease can also degrade tmRNA‐tagged proteins, but with much lower efficiency. Here, we present a unique case of enhanced recognition and degradation of an extended Mycoplasma pneumoniae ( MP ) tmRNA tag by the MP ‐Lon protease. We demonstrate that MP ‐Lon can efficiently and selectively degrade MP ‐tmRNA‐tagged proteins. Most significantly, our studies reveal that the larger (27 amino acids long) MP‐ tmRNA tag contains multiple discrete signalling motifs for efficient recognition and rapid degradation by Lon. We propose that higher‐affinity multipartite interactions between MP‐ Lon and the extended MP‐ tmRNA tag have co‐evolved from pre‐existing weaker interactions, as exhibited by Lon in E. coli , to better fulfil the function of MP‐ Lon as the sole soluble cytoplasmic protease responsible for the degradation of tmRNA‐tagged proteins.