The structure of apo ArnA features an unexpected central binding pocket and provides an explanation for enzymatic...

Area of Science:

• Biochemistry
• Structural Biology
• Microbiology

Background:

• ArnA is crucial for lipid A modification, a process essential for bacterial resistance to polymyxin antibiotics.
• Polymyxins are last-resort antibiotics against multidrug-resistant Gram-negative bacteria.
• ArnA possesses dehydrogenase and transformylase domains and forms homohexamers.

Purpose of the Study:

• To determine the crystal structure of apo ArnA.
• To compare apo ArnA structure with its ATP- and UDP-glucuronic acid-bound forms.
• To elucidate the structural basis for ArnA's cooperative function.

Main Methods:

• X-ray crystallography to obtain structures of apo ArnA and its complexes.
• Structural comparison of different ArnA states.
• Analysis of structural rearrangements and binding pocket formation.

Main Results:

• Crystal structure of apo ArnA revealed major rearrangements in the dehydrogenase domain.
• A novel central binding pocket was identified in the apo ArnA trimer, occupied by DTT.
• These rearrangements originate from the NAD(+) binding site, suggesting a regulatory mechanism.
• Conformational changes explain the reported cooperative effect in ArnA's dehydrogenase function.

Conclusions:

• Apo ArnA structure reveals a new binding pocket potentially regulated by small effector molecules.
• The findings provide a mechanistic basis for ArnA's cooperative activity.
• This structural insight could inform the development of new strategies against polymyxin-resistant bacteria.