Arabidopsis chloroplast N-terminome

ABSTRACT: Protein N-termini are prone to post translational modification and are major determinants of protein stability in bacteria, eukaryotes, and perhaps also in chloroplasts. Most chloroplast proteins undergo N-terminal maturation, but this is poorly understood due to insufficient experimental information and the N-termini of mature chloroplast proteins cannot be accurately predicted. This motivated an extensive characterization of chloroplast protein N-termini using terminal amine isotopic labeling of substrates (TAILS). Many nuclear-encoded plastid proteins accumulated with two or three different N-termini; we evaluated the significance of these different proteoforms. Ala, Val, Thr (often in N-Î? acetylated form) and Ser were the most frequently observed N-terminal residues, even after normalization for their frequency in the plastid proteome, while other residues were absent or highly under-represented. Plastid-encoded proteins showed a similar distribution of N-terminal residues, but with a higher frequency of Met. Infrequent residues such as Ile, Arg, Cys, Pro, Asp and Glu were observed for several abundant proteins likely reflecting functional regulation through their N-termini. In contrast, the thylakoid lumenal proteome showed a wide diversity of N-terminal residues, including those typically associated with instability (Asp, Glu, Leu, Phe). We propose that after cleavage of the chloroplast transit peptide by stromal processing peptidase, additional processing by unidentified peptidases occurs to avoid unstable or otherwise unfavorable N-terminal residues. The possibility of a chloroplast N-end rule is discussed. This work provides a baseline for understanding N-terminal processing and maturation of chloroplast proteins.

INSTRUMENT(S): LTQ Orbitrap

ORGANISM(S): Arabidopsis Thaliana (ncbitaxon:3702)

SUBMITTER: Klaas van Wijk  

PROVIDER: MSV000081716 | MassIVE | Tue Nov 14 14:44:00 GMT 2017

SECONDARY ACCESSION(S): PXD002476

REPOSITORIES: MassIVE