Post-translational modifications of rat liver mitochondrial outer membrane proteins identified by mass spectrometry

Abstract

SUMMARYThe identification of post-translational modifications is difficult especially for hydrophobic membrane proteins. Here we present the identification of several types of protein modifications on membrane proteins isolated from mitochondrial outer membranes. We show, in vivo, the mature rat liver mitochondrial carnitine palmitoyltransferase-I enzyme is N-terminally acetylated, phosphorylated on two threonine residues, and nitrated on two tyrosine residues. We show long chain acyl-CoA synthetase 1 is acetylated at both the N-terminal end and at a lysine residue and tyrosine residues are found to be phosphorylated and nitrated. For the three voltage-dependent anion channel isoforms present in the mitochondria, the N-terminal regions of the protein were determined and sites of phosphorylation were identified. These novel findings raise questions about regulatory aspects of carnitine palmitoyltransferase-I, long chain acyl-CoA synthetase and voltage dependent anion channel and further studies should advance our understanding about regulation of mitochondrial fatty acid oxidation in general and these three proteins in specific.

An Environment-dependent Structural Switch Underlies the Regulation of Carnitine Palmitoyltransferase 1A

“…3B), and therefore, helix ␣1 must be considered to be only partially folded under the current experimental conditions. However, we note that, due to post-translational processing, CPT1 commences with acetylated Ala 2 (49), which is an efficient helix-capping motif (50). Under in vivo conditions, the helical propensity of Ala 2 -Ala 8 in N␣ may therefore be promoted further.…”

Mitochondrial Carnitine Palmitoyltransferase 1a (CPT1a) Is Part of an Outer Membrane Fatty Acid Transfer Complex

“…The question then arises as to how VDAC can perform different transport functions and what governs its association with proteins of the mitochondrial outer and inner membranes, cytosol, and mitochondrial intermembrane space. The answer possibly lies in the fact that 1) VDAC is the most abundant protein in the MOM, representing ϳ5-10% of the total MOM protein; 2) VDAC is expressed in three isoforms (VDAC1-3), and all three isoforms are present in most tissues but in different amounts (40); and 3) all three VDAC isoforms are post-translationally modified mainly by phosphorylation and acetylation (41)(42)(43)(44).…”

Swapping of the N‐terminus of VDAC1 with VDAC3 restores full activity of the channel and confers anti‐aging features to the cell

“…In the N-end exchange VDAC3 loses alanine 13 against a serine. In VDAC1 serine 13 has been found to be a phosphorylation site in proteomic analysis [36], thus its presence may condition the function of this segment. In addition VDAC1 and 2 N-termini have, respectively, 1 or 2 additional proline and 1 or 2 additional arginine residues: these residues are the target of carbonylation reactions, while VDAC3 does not have them.…”