| First Author | Aoyama C | Year | 2011 |
| Journal | Biochem J | Volume | 440 |
| Issue | 2 | Pages | 241-50 |
| PubMed ID | 21812758 | Mgi Jnum | J:180724 |
| Mgi Id | MGI:5306884 | Doi | 10.1042/BJ20110545 |
| Citation | Aoyama C, et al. (2011) The heterotrimeric G protein subunits Galpha(q) and Gbeta(1) have lysophospholipase D activity. Biochem J 440(2):241-50 |
| abstractText | In a previous study we purified a novel lysoPLD (lysophospholipase D) which converts LPC (lysophosphatidylcholine) into a bioactive phospholipid, LPA (lysophosphatidic acid), from the rat brain. In the present study, we identified the purified 42 and 35 kDa proteins as the heterotrimeric G protein subunits Galpha(q) and Gbeta(1) respectively. When FLAG-tagged Galpha(q) or Gbeta(1) was expressed in cells and purified, significant lysoPLD activity was observed in the microsomal fractions. Levels of the hydrolysed product choline increased over time, and the Mg(2+) dependency and substrate specificity of Galpha(q) were similar to those of lysoPLD purified from the rat brain. Mutation of Galpha(q) at amino acids Lys(52), Thr(186) or Asp(205), residues that are predicted to interact with nucleotide phosphates or catalytic Mg(2+), dramatically reduced lysoPLD activity. GTP does not compete with LPC for the lysoPLD activity, indicating that these substrate-binding sites are not identical. Whereas the enzyme activity of highly purified FLAG-tagged Galpha(q) overexpressed in COS-7 cells was ~4 nmol/min per mg, the activity from Neuro2A cells was 137.4 nmol/min per mg. The calculated K(m) and V(max) values for lysoPAF (1-O-hexadecyl-sn-glycero-3-phosphocholine) obtained from Neuro2A cells were 21 muM and 0.16 mumol/min per mg respectively, similar to the enzyme purified from the rat brain. These results reveal a new function for Galpha(q) and Gbeta(1) as an enzyme with lysoPLD activity. Tag-purified Galpha(11) also exhibited a high lysoPLD activity, but Galpha(i) and Galpha(s) did not. The lysoPLD activity of the Galpha subunit is strictly dependent on its subfamily and might be important for cellular responses. However, treatment of Hepa-1 cells with Galpha(q) and Galpha(11) siRNAs (small interfering RNAs) did not change lysoPLD activity in the microsomal fraction. Clarification of the physiological relevance of lysoPLD activity of these proteins will need further studies. |
