(A) Peptide clusters covering the positive face of a growing crystal cause subsegments of the growing crystal layer to accelerate as it approaches a cluster, slow its growth as it encounters the peptides, then recover its growth rate once past the cluster. (B) A similar situation occurs on the negative crystal face, though fewer peptides clusters are present. Artist: Emily Harrington. Copyright: All rights reserved. See gallery for details.
"By producing some of the highest resolution images of peptides attaching to mineral surfaces, scientists have a deeper understanding how biomolecules manipulate the growth [of] crystals…
"The images also revealed a mechanism that molecules can use to bind to surfaces that would normally repel them. The high resolution images showed that peptides will cluster together on crystal faces that present the same electronic charge. Under certain conditions the peptides would slow down growth, while under other conditions the peptides could speed up growth.
"On another face of the crystal, where the peptides were expected to bind strongly, the researchers found instead that the peptides did not attach to the surface unless the crystal growth slowed. The peptides needed to bind in a specific way to the face, which takes more time than a non-specific attachment. As a result, the growing layers of the crystal were able to shed off the peptides as they attempted to bind.
"But when the researchers slowed down the crystal growth rate, the peptides collapsed onto the surface so strongly that they completely stopped growth. The researchers proposed that the phenomenon is due to the unique properties of bio-polymers, such as peptides or polyelectrolytes, which fluctuate in solution before resting in a stable configuration on a surface.
"'The results of the catastrophic drop in growth by peptides suggest ways that organisms achieve protection against pathological mineralization,' said Jim De Yoreo, the project lead and deputy director of research at LBNL's Molecular Foundry. 'Once growth is halted, a very high concentration of the mineral will be needed before growth can again reach significant levels.'" (EurekAlert! 2009)