Specific molecular alterations in the norpA-encoded phospholipase C of Drosophila and their effects on electrophysiological responses in vivo.
A large number of mutants in the norpA gene, which encodes the phospholipase C (PLC) involved in Drosophila phototransduction, is available for the investigation of the effects of specific amino acid substitutions in PLC on biochemical and electrophysiological properties of these mutants. Of the 47 norpA mutants screened for PLC protein content, all but one (H43) displayed drastically decreased amounts of the protein suggesting that almost any mutational alteration has a deleterious effect on the integrity of the protein. Three new amino acids were identified in the catalytic domains X and Y that are important for PLC catalytic activity and the generation of photoreceptor responses (ERG). One of them was found substituted in H43, which showed a low specific PLC activity, a pronounced decrease in ERG sensitivity, and a wild-type-like response termination time. The response termination times obtained from three mutants was found to be approximately inversely proportional to the amount of PLC. In addition, we show that (i) the specific PLC activity is a key factor determining the photoreceptor sensitivity; (ii) the catalytic activity and response termination are separable functions of PLC; and (iii) a mutation in the putative G alpha-interacting C2 domain causes a preferentially strong defect in latency.
Yoon
Jaeseung
J
Graduate School of Biotechnology, KyungHee University, Yongin City, Kyungki-Do, Korea.
Leung
Hung-Tat
HT
Lee
Seunghee
S
Geng
Chaoxian
C
Kim
Younkyung
Y
Baek
Kwanghee
K
Pak
William L
WL
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D029721:Drosophila Proteins / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000201:enzymology / Q000502:physiology*; D004594:Electrophysiology; D004596:Electroretinography; D004789:Enzyme Activation / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D054799:Phospholipase C beta; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology; D011930:Reaction Time / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D010738:Type C Phospholipases / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism*
D029721:Drosophila Proteins; D010738:Type C Phospholipases; C468371:NorpA protein, Drosophila; D054799:Phospholipase C beta