Previous studies have shown that
beta-synuclein (beta-syn), the homologue of alpha-syn, inhibited alpha-syn aggregation and stabilized Akt cell survival signaling molecule, suggesting that beta-syn was protective against alpha-syn-related
neurodegenerative disorders, such as
Parkinson's disease and
diffuse Lewy body disease. However, emerging evidence argues that the situation may be not so simple. Two missense mutations of beta-syn were identified in familial and sporadic
diffuse Lewy body disease, and wild type beta-syn was induced to form fibril structures in vitro, while, alpha-syn was shown to be protective against neurodegeneration caused by deletion of
cysteine-string protein-alpha, the presynaptic cochaperone to Hsc70 in mice. Collectively, alpha- and beta-syn are both, but in varying degrees, featured with two opposite properties, namely normal chaperone and anti-chaperone. By reviewing recent progress in syn biology with a particular focus on beta-syn, this manuscript refers to the intriguing possibility that the dual syn
proteins might have acquired a driving force for synaptic evolution. Hypothetically, the anti-chaperone syn may provoke stress-induced diverse responses, whereas, the chaperone syn may provide buffering for them, allowing accumulation of nonlethal phenotypic variations in synapses. Consequently, dual syn
proteins may cope with forthcoming stresses in the brain by stimulating adaptive evolution. In this context, failure to regulate this process due to various causes, such as gene mutations and environmental risk factors, may result in imperfect adaptability against stresses, leading to
neurodegenerative disorders.