Combinatorial biosynthesis approaches

Since the first description was only two decades ago, combinatorial biosynthesis has advanced from a limited set of proof-of-principle experiments into a more mature scientific discipline. To reach the maximal potential of natural product structural diversity, the combination of this approach with other established and emerging technologies will ultimately provide access to a rich variety of unnatural natural products with improved properties or new biological activities for future drug discovery and development. 

In summary, the combination of enzymes is advantageous from an enzymol-ogy and reachon engineering point of view. Reaction yields can be increased by avoiding product inhibition of single enzymatic reachons. Product decomposihon (e.g. by hydrolysis) can be overcome by further enzymatic transformahons. Tedious isolation of intermediate products is not necessary. However, both strategies - combinatorial biocatalysis and combinatorial biosynthesis - have their disadvantages. The in vitro approach needs every enzyme to be produced by recombinant techniques and purified in high amounts, which is in some cases difficult to achieve. On the other hand, product isolation from a biotransformation with permeabilized or whole host cells can be tedious and results in low yields. 

A major advantage of the natural products approach to drug discovery is that it is capable of providing complex molecules that would not be accessible by other routes. Compounds such as paclitaxel (Taxol, 8) or rapamycin (10) would never be prepared by standard "medicinal chemistry" approaches to drug discovery, even including the newer methods of combinatorial chemistry. Likewise, the new approach of combinatorial biosynthesis, although an important one, is unlikely in the near future to yield new compounds of the complexity of paclitaxel and camptothecin. 

Mendez C, Salas JA (2002) Engineering glycosylation in bioactive compounds by combinatorial biosynthesis. In Wohlleben W (ed) Biocombinatorial approaches for drug finding, volume 51. Springer, Heidelberg... 

PF Leadlay. Combinatorial approaches to polyketide biosynthesis. Curr Opin Chem Biol 1 162-168, 1997. 

Conformational restriction of biologically flexible molecules is a successful strategy in drug development. Application of this concept to ceramide, the membrane anchor of sphingolipids, led to the unexpected inhibition of glycosyltransferases involved in the combinatorial biosynthesis of gangliosides. This discovery offers a new approach to cell surface engineering. 

Combinatorial biosynthesis is an approach aimed at the modification of the cellular machinery involved in the biosynthetic pathways that produce natural products. There are several groups active in the field, and an example reported by McDaniel et al. (60)... 

Lee, RE, Smith, M D, Pickering, L, Fleet, G W J, An approach to combinatorial library generation of galactofuranose mimics as potential inhibitors of mycobacterial cell wall biosynthesis Synthesis of a peptidomimetic of uridine 5 -diposphogalactofuranose (UDP-galf), Tetrahedron Lett., 40, 8689 8692, 1999. 

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