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In Gram-negative bacterial cells, disulfide bond formation occurs in the oxidative environment of the periplasm and is catalysed by Dsb (disulfide bond) proteins found in the periplasm and in the inner membrane. In this report the identification of a new subfamily of disulfide oxidoreductases encoded by a gene denoted dsbI, and functional characterization of DsbI proteins from Campylobacter jejuni and Helicobacter pylori, as well as DsbB from C. jejuni, are described. The N-terminal domain of DsbI is related to DsbB proteins and comprises five predicted transmembrane segments, while the C-terminal domain is predicted to locate to the periplasm and to fold into a b-propeller structure. The dsbI gene is co-transcribed with a small ORF designated dba (dsbI-accessory). Based on a series of deletion and complementation experiments it is proposed that DsbB can complement the lack of DsbI but not the converse. In the presence of DsbB, the activity of DsbI was undetectable, hence it probably acts only on a subset of possible substrates of DsbB. To reconstruct the principal events in the evolution of DsbB and DsbI proteins, sequences of all their homologues identifiable in databases were analysed. In the course of this study, previously undetected variations on the common thiol-oxidoreductase theme were identified, such as development of an additional transmembrane helix and loss or migration of the second pair of Cys residues between two distinct periplasmic loops. In conjunction with the experimental characterization of two members of the DsbI lineage, this analysis has resulted in the first comprehensive classification of the DsbB/DsbI family based on structural, functional and evolutionary criteria.

The mono-nitrated meso-tetraphenylporphyrin (TPP) complex 2 could be readily functionalized on the substituted pyrrole ring with yields of up to 83%. These transformations were achieved via aromatic substitution with carbanions generated from diverse functionalized compounds containing different leaving groups (3a ± g, Scheme 1). The resulting TPP compounds 4a ± g, bearing two different b-substituents on the same pyrrole ring, may be further manipulated. This, in turn, should allow one to tune the solubility of TPP derivatives used in photodynamic cancer therapy.Introduction. ± Porphyrins are important compounds intensively studied in recent years [1]. From a synthetic point of view, the selective functionalization of readily available meso-tetraphenylporphyrin (TPP) and its derivatives is of significant importance due to their potential use as sensitizers in photodynamic cancer therapy [2]. We have recently published two papers describing a convenient method for the selective mono-nitration in b-position of Zn, Cu, Ni, and Co TPP complexes by means of 25 ± 50% aqueous HNO 3 in CHCl 3 [3].A NO 2 group in the ring makes porphyrins, as well as aromatic systems in general, susceptible to nucleophilic attack. Of particular importance is the nucleophilic aromatic substitution of a H-atom by a carbanion made from precursors of type XÀCH 2 ÀY, where X and Y are leaving and stabilizing groups, respectively. Mechanistically, this kind of transformation proceeds according to the vicarious nucleophilic substitution (VNS) scheme [4]. Recently, several papers concerning this type of substitution in meso-aryl rings have been published [5].