A remote surface loop modulates core structure and cold activity in phosphopantetheine adenylyltransferase

Area of Science:

• Biochemistry and Molecular Biology
• Enzymology
• Structural Biology
• Cold Adaptation Mechanisms

Background:

• Phosphopantetheine adenylyltransferase (PPAT) is vital for Coenzyme A biosynthesis and cellular metabolism.
• Understanding PPAT adaptation in psychrophilic organisms is crucial for comprehending cold-environment biochemistry.
• The specific adaptive mechanisms of PPAT in cold-loving microbes are largely unknown.

Purpose of the Study:

• To characterize the structure and function of PPAT from the psychrophilic methanotroph Methylocapsa palsarum (MpaPPAT).
• To investigate the role of a unique surface-exposed loop insertion in MpaPPAT's cold adaptation.
• To elucidate the molecular mechanisms underlying MpaPPAT's enhanced activity at low temperatures.

Main Methods:

• Sequence analysis to identify unique structural features in MpaPPAT.
• Determination of crystal structures for wild-type MpaPPAT and a loop-deletion mutant.
• Comparative biochemical assays to assess catalytic activity at varying temperatures.

Main Results:

• A unique five-amino-acid insertion (SCRLS) was identified in MpaPPAT, conserved in psychrophilic homologues.
• WT MpaPPAT exhibits high activity at 10-20 °C, while the mutant MpaPPAT(Δ67-71) shows impaired cold activity.
• Structural analysis revealed the SCRLS deletion causes allosteric changes: H4 helix rigidification and altered central pore electrostatics.

Conclusions:

• The SCRLS insertion acts as a critical allosteric modulator for MpaPPAT cold adaptation.
• This insertion maintains hexameric core flexibility and ensures a positive central channel for substrate binding at low temperatures.
• The study reveals a dual mechanism for enzymatic cold adaptation via conformational flexibility and electrostatic steering.