Enzymatic subunits

McDaniel R, Ebert-Khosla S, Hopwood DA, Khosla C. (1995). Rational design of aromatic polyketide natural products by recombinant assembiy of enzymatic subunits. Nature, 375,549-54. 

The receptor-binding site, determined by site-directed mutagenesis and the crystal structure of the PT-carbohydrate complex, is located close to the SI subunit. This suggests that PT may bind to the cell surface in such a manner that SI is positioned in dose proximity to the target cell membrane, which would be ideal for its translocation. This is in contrast to cholera toxin, where the receptor-binding portion of the B oligomer is on the opposite side from the enzymatically active A subunit (Merritt et al., 1994). It remains to be determined, however, whether the two toxins translocate their enzymatic subunits by different mechanisms. 

Unlike diphtheria toxin, little is known about the structures required for the translocation of the enzymatic subunit of PT. In diphtheria toxin and Pseudomonas aeruginosa exotoxin A, the B moiety can be clearly subdivided into two distinct domains, one responsible for receptor binding, composed essentially of (3 sheets, and one responsible for translocation of the A subunits, essentially composed of a helices (Allured etal., 1986 Choe etal., 1992). There is no clear translocation domain in PT, and much less is known about the internalization step of PT, compared to diphtheria toxin and exotoxin A. 

New compounds generated by recombinant assembly of enzymatic subunits. 

The production of cellulases by bacteria is governed by induction, catabolism repression, or end product inhibition (Kumar et al. 2008). The former mechanism also controls the constitution of cellulosome from C. thermocellum. The proteo-mic maps of the cellulose-bound protein fraction containing the cellulosomes show that the enzymatic subunits vary according to the carbon source used in the culture medium (Raman et al. 2009 Natafet al. 2010). 

Bouchier, C., Boulain, J.C., Bon, C., and Menez, A. (1991) Analysis of cDNAs encoding the two subunits of crotoxin, a phospholipase A2 neurotoxin from rattlesnake venom the acidic non enzymatic subunit derives from a phospholipase A2-like precursor. Biochim. Biophys. Acta 1088, 401-408. 

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