Molecular weights and subunit structure of LamB proteins

Area of Science:

• Molecular biology
• Structural biology
• Biophysics

Background:

• Phage lambda-receptor (LamB) proteins in Escherichia coli are crucial for nutrient transport.
• These proteins form oligomeric structures that function as transmembrane diffusion pores.
• LamB proteins exhibit selectivity for maltose and maltodextrins.

Purpose of the Study:

• To determine the molecular weight of functional oligomeric LamB proteins.
• To determine the molecular weight of dissociated LamB monomers.
• To elucidate the subunit composition of functional LamB protein aggregates.

Main Methods:

• Sedimentation equilibrium analysis was employed.
• Experiments were conducted in homogeneous non-ionic surfactant and deuterium oxide for oligomers.
• Dissociated monomers were analyzed in 6 M guanidine-HCl.

Main Results:

• The molecular weight of functional oligomers was determined to be 135,600.
• The molecular weight of dissociated monomers was found to be 45,900.
• The data indicates that functional LamB proteins consist of three identical subunits.

Conclusions:

• Functional LamB proteins exist as trimers.
• Each functional unit is composed of three identical subunits.
• This trimeric structure is essential for the formation of transmembrane diffusion pores.