SCAN: Enzymes of tetrapyrrole biosynthesis

SCAN

Title: Enzymes of tetrapyrrole biosynthesis: study of the early steps of the pathway in Desulfovibrio vulgaris Hildenborough

Speaker: Susana Lobo,

Laboratory: Molecular Genetics of Microbial Resistance Lab

Abstract
The biosynthesis of the modified tetrapyrroles in the sulphate reducer Desulfovibrio vulgaris Hildenborough has been investigated by characterization of the enzymes required for the transformation of 5-aminolevulinic acid into Co-sirohydrochlorin. Porphobilinogen synthase (HemB) was found to be a homohexamer and a zinc-dependent enzyme. Porphobilinogen deaminase (HemC) was shown to contain the dipyrromethane cofactor. Uroporphyrinogen III synthase is found fused with uroporphyrinogen III methyltransferase (HemD-CobA). Both activities were confirmed in the fused protein and the individual enzyme activities were tested separately after dissection of the gene that allowed the production of two distinct proteins. A gene annotated on the genome as a bifunctional precorrin-2 dehydrogenase and sirohydrochlorin ferrochelatase was shown to be only capable of synthesizing sirohydrochlorin, i.e. it only holds the dehydrogenase activity. Two CbiK cobaltochelatases are also encoded by D. vulgaris genome. Our results showed that one enzyme is cytoplasmic (CbiKC) and the other one is periplasmic (CbiKP). CbiKP revealed the presence of a haem b, so far, unique in the chelatase family of enzymes. Both CbiKC and CbiKP enzymes perform in vitro cobalt and iron chelation into sirohydrochlorin yielding Co-sirohydrochlorin or siroheam, respectively.

Short CV
1999 to 2004 - Degree in Biology by Universidade Lusófona de Humanidades e Tecnologias
September 2003 to July 2004 - Undergraduate training at Metalloproteins and Bioenergetics Lab and at Molecular Genetics of Microbial Resistance Lab (TQB) under the supervision of Dr. Ana Melo and co-supervision of Dr. Lígia M. Saraiva.
Since January 2005 - PhD fellowship by FCT at Molecular Genetics of Microbial Resistance Lab (ITQB) supervised by Dr. Lígia M. Saraiva and co-supervised by Prof. Miguel Teixeira.