NMR structure of calmodulin complexed to an N-terminally acetylated ?-synuclein peptide.

ABSTRACT: Calmodulin (CaM) is a calcium binding protein that plays numerous roles in Ca-dependent cellular processes, including uptake and release of neurotransmitters in neurons. ?-Synuclein (?-syn), one of the most abundant proteins in central nervous system neurons, helps maintain presynaptic vesicles containing neurotransmitters and moderates their Ca-dependent release into the synapse. Ca-Bound CaM interacts with ?-syn most strongly at its N-terminus. The N-terminal region of ?-syn is important for membrane binding; thus, CaM could modulate membrane association of ?-syn in a Ca-dependent manner. In contrast, Ca-free CaM has negligible interaction. The interaction with CaM leads to significant signal broadening in both CaM and ?-syn NMR spectra, most likely due to conformational exchange. The broadening is much reduced when binding a peptide consisting of the first 19 residues of ?-syn. In neurons, most ?-syn is acetylated at the N-terminus, and acetylation leads to a 10-fold increase in binding strength for the ?-syn peptide (KD = 35 ± 10 ?M). The N-terminally acetylated peptide adopts a helical structure at the N-terminus with the acetyl group contacting the N-terminal domain of CaM and with less ordered helical structure toward the C-terminus of the peptide contacting the CaM C-terminal domain. Comparison with known structures shows that the CaM/?-syn complex most closely resembles Ca-bound CaM in a complex with an IQ motif peptide. However, a search comparing the ?-syn peptide sequence with known CaM targets, including IQ motifs, found no homologies; thus, the N-terminal ?-syn CaM binding site appears to be a novel CaM target sequence.

SUBMITTER: Gruschus JM 

PROVIDER: S-EPMC3758425 | biostudies-literature | 2013 May

REPOSITORIES: biostudies-literature