Isolation and Sequencing of Salsolinol Synthase, an Enzyme Catalyzing Salsolinol Biosynthesis

Abstract

Salsolinol (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline), a derivate of dopamine, is suspected to be the most probable neurotoxin in the degeneration of dopaminergic neurons. Numerous hypotheses regarding its pathophysiological roles have been raised, especially related to Parkinson's disease and alcohol addiction. In the mammalian brain, salsolinol may be enzymatically synthesized by salsolinol synthase from dopamine and acetaldehyde. However, the direct evidence of its biosynthesis was still missing. In this study, we purified salsolinol synthase from rat brain by a systematical procedure involving acid precipitation, ultrafiltration, and hydrophilic interaction chromatography. The molecular weight of salsolinol synthase determined by MALDI-TOF MS is 8622.29 Da, comprising 77 amino acids (MQIFVKTLTG KTITLEVEPS DTIKNVKAKI QDKEGIPPDQ QRLIFAGKQL EDGRTLSDYN IQKKSTLHLV LRLRVDY). Homology analysis showed that the enzyme is a ubiquitin-like protein, with a difference of four amino acids, which suggests it is a novel protein. After it was overexpressed in eukaryotic cells, the production of salsolinol was significantly increased as compared with control, confirming the catalytic function of this enzyme. To our knowledge, it is the first systematic purification and sequencing of salsolinol synthase. Together, this work reveals a formerly anonymous protein and urges further exploration of its possible prognostic value and implications in Parkinson's disease and other related disorders.

Not Just from Ethanol. Tetrahydroisoquinolinic (TIQ) Derivatives: from Neurotoxicity to Neuroprotection

“…For many years, mostly due to limitations of the available analytical methods, it was thought that (R)-salsolinol should be the only enantiomer present in human brain tissue. In this respect, it has been reported that the R-enantiomer predominates in urines of healthy volunteers, whereas the S-enantiomer predominates in port wine and possibly in other beverages and foods, suggesting that salsolinol present in human bodies could have, at least partially, an endogenous enzymatic origin (Chen et al 2018), as previously suggested by Collins et al (1990). These experiments have shown that co-administration of small doses of L-DOPA with the ethanol/liquid diet led to an increased striatal concentration of salsolinol as shown in Fig.…”

“…As racemic mixture of enantiomers, salsolinol can be formed non-enzymatically by the Pictet-Spengler reaction of DA with acetaldehyde ( Fig. 2) (Cohen and Collins 1970) or from pyruvic acid followed by decarboxylation (Dostert et al 1988;Chen et al 2018). Whilst, the stereo-selective enzymatic synthesis from DA via (R)-salsolinol synthase is supposed to generate the (R)-enantiomer ( Fig.…”

“…Whilst, the stereo-selective enzymatic synthesis from DA via (R)-salsolinol synthase is supposed to generate the (R)-enantiomer ( Fig. 3) (Chen et al 2018;Naoi et al 1996).…”

“…Salsolinol was also thought responsible of contributing to degeneration of DArgic neurons in the onset and progression of parkinsonism (Chen et al 2018). On the other hand, Krygowska-Wajs and collaborators (Krygowska-Wajs et al 1997) reported that the levels of endogenous salsolinol were correlated to the degree of PD and cannot be affected by L-DOPA treatment in patients with different degrees of parkinsonism (Krygowska-Wajs et al 1997).…”

Synthesis and Antimicrobial Activity of Novel Piperidinyl Tetrahydrothieno[2,3-c]isoquinolines and Related Heterocycles

“…Anal. Calcd for C23 H 27 N 3 O 2 S (409.55): C, 67.45; H, 6.65; N, 10.26; S, 7.83%. Found: C, 67.33; H, 6.55; N, 10.16; S, 7.71%.…”