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Function(s) and Biological Relevance

The protein being studied is Tetrahydroprotoberberine N-methyltransferase. This protein is found in yellow horned poppy (Glaucium flavium) and gives insights into substrate recognition and catalysis for the rational engineering of enzymes for chemoenzymatic synthesis and metabolic engineering. The substrate specificity of Tetrahydroprotoberberine N-methyltransferase arises from the arrangement of subgroup-specific stereospecific recognition elements relative to catalytic elements that are more widely-conserved among all Benzylisoquinoline alkaloids (BIA) N-methyltransferases (NMT).

Broader Implications

Tetrahydroprotoberberine N-methyltransferase is relevant because of the importance and utility of Benzylisoquinoline alkaloids (BIA) compounds such as the use of metabolic engineering and synthetic biology approaches to reconstitute portions of the BIA biosynthetic pathways. However, most experiments have not provided substantial proof and explanations. In order to address this central problem in metabolic engineering, fundamental molecular, structural, and functional studies of BIA enzymes are needed.

Structural highlights and structure-function relationships

Tetrahydroprotoberberine N-methyltransferase contains a which is composed of the following amino acids, Glu-204, Glu-207 and His-208. Although the authors acknowledged the importance of the amino groups and the mechanisms of catalysis, they also acknowledged that other roles consistent with the structures and mutagenesis data are possible. This catalytic triad is important and facilitates the protein with difficult reactions. The spacefill view of the protein allows the readers to get an overall view of the protein in different colors. The protein consists of a hydrophilic side chains as well as hydrophobic side chains. The hydrophobic interactions are seen at the top of the L-shaped binding pocket for the ligand SAM, consisting of hydrophobic side chains of Ile-234, Phe-243, Phe-257, Val-262, Met-290 and Phe-340 forming an "isoquinoline pocket". The hydrophilic side chains of the ligand form a catalytic pocket that surrounds the amino group as well as the methyl donor of the ligand. The protein consists of an active site which is made up of Val-188, Asp-187 and Ala-186. This active site allows the binding of the tetrahydroprotoberberine substrates as well as participates in the formation and breakdown of the transition states.

Energy Transformation

There are no energy transformation for this protein.