Preincubation of t-SNAREs with Complexin I Increases Content-Mixing Efficiency.
Complexin (Cpx) is a major regulator for Ca(2+)-triggered fast neuroexocytosis which underlies neuronal communication. Many psychiatric and neurological disorders accompany changes in the Cpx expression level, suggesting that abnormal Cpx levels may elicit aberrant cognitive symptoms. To comprehend how the changes in the Cpx level might affect neuronal communication, we investigated Ca(2+)-triggered exocytosis at various Cpx concentrations. Ca(2+)-triggered content-mixing between a single proteoliposome of t-SNARE and another single proteoliposome of v-SNARE plus Ca(2+)-sensor synaptotagmin 1 was examined with total internal reflection microscopy. We find that Cpx enhances Ca(2+)-triggered vesicle fusion with the yield changing from approximately 10% to 70% upon increasing Cpx from 0 to 100 nM. Unexpectedly, however, the fusion efficiency becomes reduced when Cpx is increased further, dropping to 20% in the micromolar range, revealing a bell-shaped dose-response curve. Intriguingly, we find that the rate of vesicle fusion is nearly invariant through the entire range of Cpx concentrations studied, suggesting that a reevaluation of the current Cpx clamping mechanism is necessary. Thus, our results provide insights into how delicately Cpx fine-tunes neuronal communication.
Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University , Ames, Iowa 50011, United States.
Jaewook
J
Kim
Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University , Ames, Iowa 50011, United States.
Yicheng
Y
Zhu
Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University , Ames, Iowa 50011, United States.
Yeon-Kyun
YK
Shin
D033942:Adaptor Proteins, Vesicular Transport / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D005089:Exocytosis / Q000502:physiology*; D008561:Membrane Fusion; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D050600:SNARE Proteins / Q000378:metabolism*; D013572:Synaptic Vesicles / Q000378:metabolism*
D033942:Adaptor Proteins, Vesicular Transport; D009419:Nerve Tissue Proteins; D050600:SNARE Proteins; C095992:complexin I; D002118:Calcium