Neuronal protein that plays several roles in synaptic activity such as regulation of synaptic vesicle trafficking and subsequent neurotransmitter release (By similarity). Participates as a monomer in synaptic vesicle exocytosis by enhancing vesicle priming, fusion and dilation of exocytotic fusion pores (By similarity). Mechanistically, acts by increasing local Ca(2+) release from microdomains which is essential for the enhancement of ATP-induced exocytosis (By similarity). Acts also as a molecular chaperone in its multimeric membrane-bound state, assisting in the folding of synaptic fusion components called SNAREs (Soluble NSF Attachment Protein REceptors) at presynaptic plasma membrane in conjunction with cysteine string protein-alpha/DNAJC5 (By similarity). This chaperone activity is important to sustain normal SNARE-complex assembly during aging (By similarity). Also plays a role in the regulation of the dopamine neurotransmission by associating with the dopamine transporter (DAT1) and thereby modulating its activity (By similarity). Soluble monomer. Homotetramer. A dynamic intracellular population of tetramers and monomers coexists normally and the tetramer plays an essential role in maintaining homeostasis (By similarity). Interacts with UCHL1 (By similarity). Interacts with phospholipase D and histones. Interacts (via N-terminus) with synphilin-1/SNCAIP; this interaction promotes formation of SNCA inclusions in the cytoplasm. Interacts with CALM1. Interacts with STXBP1; this interaction controls SNCA self-replicating aggregation. Interacts with SNARE components VAMP2 and SNAP25; these interactions allows SNARE complex assembly and integrity (By similarity). Interacts with RPH3A and RAB3A (By similarity). Interacts with SERF1A; this interaction promotes the aggregation of SNCA (By similarity). Interacts with SEPTIN4 (By similarity). Membrane-bound in dopaminergic neurons (By similarity). Expressed and colocalized with SEPTIN4 in dopaminergic axon terminals, especially at the varicosities (By similarity). Phosphorylated, predominantly on serine residues. Acetylation at Met-1 seems to be important for proper folding and native oligomeric structure. Ubiquitinated. The predominant conjugate is the diubiquitinated form. Belongs to the synuclein family.