title: Self-Assembly of Protein Nanofibrils Orchestrates Calcite Step Movement through Selective Nonchiral Interactions.
abstract: The recognition of atomically distinct surface features by adsorbed biomolecules is central to the formation of surface-templated peptide or protein nanostructures. On mineral surfaces such as calcite, biomolecular recognition of, and self-assembly on, distinct atomic kinks and steps could additionally orchestrate changes to the overall shape and symmetry of a bulk crystal. In this work, we show through in situ atomic force microscopy (AFM) experiments that an acidic 20 kDa cement protein from the barnacle Megabalanus rosa (MRCP20) binds specifically to step edge atoms on {101̅4} calcite surfaces, remains bound and further assembles over time to form one-dimensional nanofibrils. Protein nanofibrils are continuous and organized at the nanoscale, exhibiting striations with a period of ca. 45 nm. These fibrils, templated by surface steps of a preferred geometry, in turn selectively dissolve underlying calcite features displaying the same atomic arrangement. To demonstrate this, we expose the protein solution to bare and fibril-associated rhombohedral etch pits to reveal that nanofibrils accelerate only the movement of fibril-forming steps when compared to undecorated steps exposed to the same solution conditions. Calcite mineralized in the presence of MRCP20 results in asymmetric crystals defined by frustrated faces with shared mirror symmetry, suggesting a similar step-selective behavior by MRCP20 in crystal growth. As shown here, selective surface interactions with step edge atoms lead to a cooperative regime of calcite modification, where templated long-range protein nanostructures shape crystals.
authors.affiliation: †Chemistry Division, US Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375, United States.
authors.forename: Christopher R
authors.initials: CR
authors.lastname: So
authors.affiliation: ‡Center for Bio/Molecular Science and Engineering, US Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375, United States.
authors.forename: Jinny
authors.initials: J
authors.lastname: Liu
authors.affiliation: †Chemistry Division, US Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375, United States.
authors.forename: Kenan P
authors.initials: KP
authors.lastname: Fears
authors.affiliation: ‡Center for Bio/Molecular Science and Engineering, US Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375, United States.
authors.forename: Dagmar H
authors.initials: DH
authors.lastname: Leary
authors.affiliation: ‡Center for Bio/Molecular Science and Engineering, US Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375, United States.
authors.forename: Joel P
authors.initials: JP
authors.lastname: Golden
authors.affiliation: †Chemistry Division, US Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375, United States.
authors.forename: Kathryn J
authors.initials: KJ
authors.lastname: Wahl
mesh_terms: D000818:Animals; D002119:Calcium Carbonate / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D057139:Nanofibers / Q000737:chemistry*; D010316:Particle Size; D011506:Proteins / Q000737:chemistry*; D013499:Surface Properties; D001468:Thoracica / Q000737:chemistry
chemical_list: D011506:Proteins; D002119:Calcium Carbonate
keywords: adsorption; atomic force microscopy; calcite; molecular self-assembly; nanofibril; proteins