Measurements Of Protein Surface Verify Electrostatics Model

December 03, 1998

CHAMPAIGN, Ill. - Using a surface-force apparatus, researchers at the University of Illinois have measured the electrostatic properties of a protein surface at the molecular level. Their results provide the first direct comparison between localized measurements and theoretical predictions.

"We obtained direct measurements of the pH-dependent electrostatic charge density of a single binding face of the protein streptavidin," said Deborah Leckband, a U. of I. professor of chemical engineering. "Our measurements show excellent agreement with values predicted from theory, thus verifying the accuracy of our measurement technique."

Identifying the electrostatic properties of a protein surface is useful for interpreting biochemical data and for obtaining a better mechanistic understanding of the forces that govern a protein's behavior. Many researchers believe, for example, that complementary charge distributions can generate steering torques that act like tiny tractor beams that pull proteins into the right orientation for binding.

To probe the local surface charges, Leckband, biophysics professor Shankar Subramaniam and graduate research assistant Sanjeevi Sivasankar first prepared homogeneously oriented monolayers of streptavidin by anchoring the protein to a supported lipid bilayer.

Using a surface-force apparatus, they then measured directly the electrostatic surface potential of the protein monolayer at a variety of pH levels. They were thus able to isolate the point of zero charge for the binding face of the protein. Importantly, the measured value for the exposed protein surface differed from the point of zero charge for the net protein.

"The difference in the pH-dependence between the probed surface and the soluble protein clearly demonstrates that these force measurements indeed reflect the local charge density of the oriented protein, rather than its net charge," Leckband said.

The experimentally measured surface-charge densities were then compared with theoretical predictions of the electrostatic potential distribution around the protein surface.

"The calculated values agreed very closely with those obtained by the surface-force measurements," Leckband said. "This tells us not only that we can measure the local properties of protein surfaces at the molecular level, but also that current models are reasonably accurate."

While the study focused on the pH-dependence of electrostatic surface-charge densities, "this direct approach to probing the electrostatic features of proteins is applicable to investigations of any perturbation that alters the electrostatic composition of the surfaces of immobilized macromolecules," Leckband said.

The researchers announced their findings in the October issue of the Proceedings of the National Academy of Sciences.

University of Illinois at Urbana-Champaign

Related Protein Articles from Brightsurf:

The protein dress of a neuron
New method marks proteins and reveals the receptors in which neurons are dressed

Memory protein
When UC Santa Barbara materials scientist Omar Saleh and graduate student Ian Morgan sought to understand the mechanical behaviors of disordered proteins in the lab, they expected that after being stretched, one particular model protein would snap back instantaneously, like a rubber band.

Diets high in protein, particularly plant protein, linked to lower risk of death
Diets high in protein, particularly plant protein, are associated with a lower risk of death from any cause, finds an analysis of the latest evidence published by The BMJ today.

A new understanding of protein movement
A team of UD engineers has uncovered the role of surface diffusion in protein transport, which could aid biopharmaceutical processing.

A new biotinylation enzyme for analyzing protein-protein interactions
Proteins play roles by interacting with various other proteins. Therefore, interaction analysis is an indispensable technique for studying the function of proteins.

Substituting the next-best protein
Children born with Duchenne muscular dystrophy have a mutation in the X-chromosome gene that would normally code for dystrophin, a protein that provides structural integrity to skeletal muscles.

A direct protein-to-protein binding couples cell survival to cell proliferation
The regulators of apoptosis watch over cell replication and the decision to enter the cell cycle.

A protein that controls inflammation
A study by the research team of Prof. Geert van Loo (VIB-UGent Center for Inflammation Research) has unraveled a critical molecular mechanism behind autoimmune and inflammatory diseases such as rheumatoid arthritis, Crohn's disease, and psoriasis.

Resurrecting ancient protein partners reveals origin of protein regulation
After reconstructing the ancient forms of two cellular proteins, scientists discovered the earliest known instance of a complex form of protein regulation.

Sensing protein wellbeing
The folding state of the proteins in live cells often reflect the cell's general health.

Read More: Protein News and Protein Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to