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 (PubMed:12408865). 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). Additional isoforms seem to exist. Found only in brain (hippocampus, brainstem and cortex). Specifically expressed in neuronal cell bodies and synapses. Phosphorylated, predominantly on serine residues. Phosphorylated on Tyr-125 upon osmotic stress. Ubiquitinated. The predominant conjugate is the diubiquitinated form. Acetylation at Met-1 seems to be important for proper folding and native oligomeric structure. Belongs to the synuclein family.