Proteins at Liquid Interfaces

Being made of both hydrophilic and hydrophobic amino acids proteins are intrinsically amphiphilic molecules and will readily adsorb onto interfaces between water and non-polar fluids (such as oil-water and air-water interfaces). In most biological systems this is typically avoided as changes in protein structure that occurs is typically associated with a loss in function. Adsorption onto such interfaces, however, is often unavoidable in industrial and biotechnological processes so understanding the link between protein function and structure at interfaces is important in the applications of proteins and other biomolecules.

S‌napshots taken from simulation of HFBII hydrophobin at water-octane interface (taken from DL Cheung, Langmuir, 28, 8730, 2012)

In order to investigate this link the group is currently using molecular dynamics simulation to investigate proteins at fluid interfaces. Initilly this focused on biosurfactant proteins (proteins that act as detergents) such as the hydrophobins. Using simulation we have investigated that link between the structure of these proteins and their interfacial behaviour, in particular examining the effect of their amphiphilic surface structure on the strength of their adsorption at an oil-water interface.

‌Effect of surface structure on interface between HFBII and water-octane interface (taken from DL Cheung, Langmuir, 28,8730, 2012)

More recently we have started investigating protein structure at liquid interfaces. When a protein adsorbs onto a liquid interface it will commonly undergo conformational change, as the hydrophobic amino acids that normally reside in the core of protein partition into the hydrophobic (air/oil/etc) medium. The try to understand the link between protein structure and interfacial conformation and function we performed simulations of some peptides derived from the protein myoglobin. For the two peptides we investigated we found that these exhibited a number of different conformations at the air-water interface; these different conformations were similar in energy to each other but separated by relatively large energy barriers. One of these, consisting of the first 55 residues of the full protein, typically formed extended conformations. The other peptide was more commonly found in compact states. This difference in the preferred conformation is consistent with the differing emulsification properties of these proteins, as the first protein was found to be a more effective emulsifier than the second.

Conformations of myoglobin-derived peptides at air-water interface (taken from DL Cheung, Langmuir, 32, 4405, 2016)