title: How fluorescent labelling alters the solution behaviour of proteins.
abstract: A complete understanding of the role of molecular anisotropy in directing the self assembly of colloids and proteins remains a challenge for soft matter science and biophysics. For proteins in particular, the complexity of the surface at a molecular level poses a challenge for any theoretical and numerical description. A soft matter approach, based on patchy models, has been useful in describing protein phase behaviour. In this work we examine how chemical modification of the protein surface, by addition of a fluorophore, affects the physical properties of protein solutions. By using a carefully controlled experimental protein model (human gamma-D crystallin) and numerical simulations, we demonstrate that protein solution behaviour defined by anisotropic surface effects can be captured by a custom patchy particle model. In particular, the chemical modification is found to be equivalent to the addition of a large hydrophobic surface patch with a large attractive potential energy well, which produces a significant increase in the temperature at which liquid-liquid phase separation occurs, even for very low fractions of fluorescently labelled proteins. These results are therefore directly relevant to all applications based on the use of fluorescent labelling by chemical modification, which have become increasingly important in the understanding of biological processes and biophysical interactions.
authors.affiliation: Department of Chemistry, Maynooth University, Maynooth, Co. Kildare, Ireland. jennifer.mcmanus@nuim.ie.
authors.forename: M K
authors.initials: MK
authors.lastname: Quinn
authors.affiliation: CNR-ISC UOS Sapienza, Piazzale A. Moro 2, 00186 Roma, Italy.
authors.forename: N
authors.initials: N
authors.lastname: Gnan
authors.affiliation: Department of Chemistry, Maynooth University, Maynooth, Co. Kildare, Ireland. jennifer.mcmanus@nuim.ie.
authors.forename: S
authors.initials: S
authors.lastname: James
authors.affiliation: Dipartimento di Fisica, "Sapienza" Universita' di Roma, Piazzale A. Moro 2, 00186, Roma, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Ninarello
authors.affiliation: CNR-ISC UOS Sapienza, Piazzale A. Moro 2, 00186 Roma, Italy and Dipartimento di Fisica, "Sapienza" Universita' di Roma, Piazzale A. Moro 2, 00186, Roma, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Sciortino
authors.affiliation: CNR-ISC UOS Sapienza, Piazzale A. Moro 2, 00186 Roma, Italy and Dipartimento di Fisica, "Sapienza" Universita' di Roma, Piazzale A. Moro 2, 00186, Roma, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Zaccarelli
authors.affiliation: Department of Chemistry, Maynooth University, Maynooth, Co. Kildare, Ireland. jennifer.mcmanus@nuim.ie.
authors.forename: J J
authors.initials: JJ
authors.lastname: McManus
mesh_terms: D002942:Circular Dichroism; D016650:Fluorescein-5-isothiocyanate / Q000737:chemistry; D005456:Fluorescent Dyes / Q000737:chemistry*; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D012996:Solutions / Q000737:chemistry; D013499:Surface Properties; D044366:Transition Temperature; D038222:gamma-Crystallins / Q000737:chemistry*
chemical_list: C504903:CRYGD protein, human; D005456:Fluorescent Dyes; D012996:Solutions; D038222:gamma-Crystallins; D016650:Fluorescein-5-isothiocyanate