Bacterial and other biological systems for polyester production

Introduction

• most bacteria and family Halobactericeae of Archae can synthesize PHA
• function of PHA in cells: storage compound (it is polyester)
• in a form of: insoluble inclusions in cytoplasm
• it is synthesized when:
  

1. abundant in carbon source
2. low of other nutrient (eg. N, P, S, O)

• uses in the industry:

1. source for synthesis of enantiomerically pure chemicals
2. raw materials for production of paint

Biosynthetic Pathways

• key enzyme: PHA synthase (also known as PhaC or PhaEC)
  
• for Ralstonia eutropha:
  

acetyl-CoA is utilise to produce PHB via -R(-)-3-hydroxybutyryl-CoA. it uses 3-step pathway with B-ketothiolase (it is NADPH-dependent acetoacetyl-CoA reductase) & PHA synthase

• acetyl-CoA is the central intermediate in metabolism of any organism. thus, it can be formed from any carbon sources (eg. carbohydrate & fatty acid)

PHA synthase

• PHA synthase in R.eutropha is in class I
• the classes are based on:

1. the number of different subunits that constitute the active PHA-synthase protein
2. substrate range

• site-directed mutagenesis: a method used to identify & confirm the extended homologies that are

1. shared by all PHA synthases & presumed
2. presumed important to the catalytic cycle of PHA synthases

• in R.eutropha: cys-319 in CXCXGG motif is needed for:

1. PHA synthase activity
2. provide 1 of the 2 thiols groups thought to be important for the proposed catalytic cycle