Mitochondrial GPAT1 is most active in OMM but not in mitochondrial associated vesicles (MAV)

PELLON-MAISON, M.; MONTANARO, M.A.; COLEMAN, R.A.; GONZALEZ-BARO, M.R.

Rosario, Argentina

Congreso; XLII Reunión Anual de la Sociedad Argentina de Investigación Bioquímica (SAIB); 2006

SAIB

            Glycerol 3-phosphate acyltransferase-1 (GPAT1), catalyzes the committed step in glycerolipid synthesis.  Both GPAT1 and carnitine-palmitoyltransferase 1 (CPT1) are located on the outer mitochondrial membrane (OMM) and their reciprocal regulation may control acyl-CoA metabolism at the OMM. To determine whether GPAT1, like CPT1, is enriched in both mitochondrial contact sites (CS) and OMM, and to correlate protein location and enzymatic function, we obtained rat liver submitochondrial fractions.  Most GPAT1 protein was present in a vesicular fraction associated with mitochondria (MAV) but GPAT specific activity in this fraction was low.  In contrast, highest GPAT1 specific activity was present in OMM from purified mitochondria. Contact sites from crude mitochondria (ER-CS) also showed high GPAT1 expression but low specific activity.To determine how GPAT1 is targeted to mitochondria, recombinant protein was synthesized in vitro and its incorporation into crude and purified mitochondria was assayed.  GPAT1 was rapidly incorporated into mitochondria, but not into microsomes. Incorporation was ATP-driven and GPAT1 became an integral membrane protein after incorporation.  These results demonstrate that two pools of GPAT1 are present in rat liver mitochondria: an active one, located in OMM and a less active one, located in membranes (ER-CS and MAV) associated with both mitochondria and ER.