Structural basis of enzymatic (S)-norcoclaurine biosynthesis.
The enzyme norcoclaurine synthase (NCS) catalyzes the stereospecific Pictet-Spengler cyclization between dopamine and 4-hydroxyphenylacetaldehyde, the key step in the benzylisoquinoline alkaloid biosynthetic pathway. The crystallographic structure of norcoclaurine synthase from Thalictrum flavum in its complex with dopamine substrate and the nonreactive substrate analogue 4-hydroxybenzaldehyde has been solved at 2.1A resolution. NCS shares no common features with the functionally correlated "Pictet-Spenglerases" that catalyze the first step of the indole alkaloids pathways and conforms to the overall fold of the Bet v1-like protein. The active site of NCS is located within a 20-A-long catalytic tunnel and is shaped by the side chains of a tyrosine, a lysine, an aspartic, and a glutamic acid. The geometry of the amino acid side chains with respect to the substrates reveals the structural determinants that govern the mechanism of the stereoselective Pictet-Spengler cyclization, thus establishing an excellent foundation for the understanding of the finer details of the catalytic process. Site-directed mutations of the relevant residues confirm the assignment based on crystallographic findings.
Ilari
Andrea
A
Dipartimento di Scienze Biochimiche and Istituto di Biologia e Patologia Molecolari, CNR, Sapienza University, Piazzale Aldo Moro 5, 00185 Roma, Italy.
Franceschini
Stefano
S
Bonamore
Alessandra
A
Arenghi
Fabio
F
Botta
Bruno
B
Macone
Alberto
A
Pasquo
Alessandra
A
Bellucci
Luca
L
Boffi
Alberto
A
D000470:Alkaloids / Q000096:biosynthesis* / Q000737:chemistry*; D055162:Biocatalysis; D019731:Carbon-Nitrogen Ligases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D044005:Tetrahydroisoquinolines / Q000737:chemistry*; D031949:Thalictrum / Q000201:enzymology* / Q000235:genetics
D000470:Alkaloids; D044005:Tetrahydroisoquinolines; D019731:Carbon-Nitrogen Ligases; C450500:norcoclaurine synthase; C012348:higenamine