Structure--function studies of the recombinant protein bioemulsifier AlnA

Area of Science:

• Microbiology
• Biochemistry
• Protein Engineering

Background:

• Acinetobacter radioresistens KA53 produces alasan, an extracellular bioemulsifier.
• The active component is a 35.77 kDa protein, AlnA, homologous to Escherichia coli outer membrane protein A (OmpA).
• E. coli OmpA lacks emulsifying activity despite high sequence homology with AlnA.

Purpose of the Study:

• To investigate the structure-function relationship of the protein bioemulsifier AlnA.
• To identify the specific regions responsible for AlnA's emulsifying activity.
• To understand the mechanism by which AlnA prevents oil droplet coalescence.

Main Methods:

• Site-directed polymerase chain reaction (PCR) mutagenesis was used to create mutations in AlnA's hydrophobic regions.
• Overlap PCR method was employed for constructing deletions and substitutions.
• Emulsifying activities of mutated AlnA proteins were analyzed.
• Adhesion of mutated proteins to hexadecane was assessed.

Main Results:

• All four identified hydrophobic regions in AlnA are essential for its emulsifying activity.
• Mutated AlnA proteins, even inactive ones, retained avid adherence to hexadecane.
• The findings suggest a dual role for AlnA: hydrocarbon binding and specific structural formation.

Conclusions:

• The four hydrophobic regions are critical for AlnA's bioemulsifier function.
• Emulsification requires more than just hydrocarbon binding; it involves forming a structure that prevents oil droplet coalescence.
• This study provides the first structure-function analysis of a protein bioemulsifier.