X-ray structure of prephenate dehydratase from Streptococcus mutans

Area of Science:

• Biochemistry
• Enzymology
• Structural Biology

Background:

• Prephenate dehydratase is a key enzyme in the shikimate pathway for L-phenylalanine biosynthesis, absent in mammals, making it a potential drug target for antibiotics and herbicides.
• This enzyme is allosteric, meaning its activity is regulated by end products like phenylalanine, and it possesses distinct catalytic (PDT) and regulatory (ACT) domains.
• Typically, prephenate dehydratase exists in an open, active conformation when unbound to phenylalanine and a closed, inhibited conformation when bound.

Purpose of the Study:

• To investigate the structural basis of prephenate dehydratase regulation, particularly in Streptococcus mutans.
• To determine the conformation of prephenate dehydratase from Streptococcus mutans (Sm-PDT) in the absence of its allosteric effector, phenylalanine.
• To explore alternative mechanisms for the allosteric regulation of prephenate dehydratase.

Main Methods:

• X-ray crystallography was employed to determine the three-dimensional structure of prephenate dehydratase from Streptococcus mutans (Sm-PDT).
• Structural analysis focused on the conformation of the catalytic site in relation to the regulatory domain.
• Comparison of the Sm-PDT structure with known structures of prephenate dehydratase in different states (e.g., Sa-PDT, Ct-PDT).

Main Results:

• The crystal structure of Sm-PDT revealed a closed, inhibited conformation of the catalytic site even without phenylalanine bound to the regulatory site.
• This finding contrasts with the expected open conformation of the enzyme in the absence of the allosteric effector.
• The observed structure suggests that phenylalanine binding may not be the sole factor inducing the closed conformation in Sm-PDT.

Conclusions:

• The regulation of prephenate dehydratase may involve mechanisms beyond simple allosteric binding of phenylalanine.
• The Streptococcus mutans prephenate dehydratase structure provides new insights into the conformational flexibility and regulatory strategies of this enzyme class.
• Further studies are warranted to elucidate the precise allosteric mechanism governing the activity of Sm-PDT.