title: Protein aggregation probed by two-photon fluorescence correlation spectroscopy of native tryptophan.
abstract: Fluorescence correlation spectroscopy (FCS) has proven to be a powerful tool for the study of a range of biophysical problems including protein aggregation. However, the requirement of fluorescent labeling has been a major drawback of this approach. Here we show that the intrinsic tryptophan fluorescence, excited via a two-photon mechanism, can be effectively used to study the aggregation of tryptophan containing proteins by FCS. This method can also yield the tryptophan fluorescence lifetime in parallel, which provides a complementary parameter to understand the aggregation process. We demonstrate that the formation of soluble aggregates of barstar at pH 3.5 shows clear signatures both in the two-photon tryptophan FCS data and in the tryptophan lifetime analysis. The ability to probe the soluble aggregates of unmodified proteins is significant, given the major role played by this species in amyloid toxicity.
authors.affiliation: Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India.
authors.forename: Bankanidhi
authors.initials: B
authors.lastname: Sahoo
authors.forename: J
authors.initials: J
authors.lastname: Balaji
authors.forename: Suman
authors.initials: S
authors.lastname: Nag
authors.forename: Sanjeev Kumar
authors.initials: SK
authors.lastname: Kaushalya
authors.forename: Sudipta
authors.initials: S
authors.lastname: Maiti
mesh_terms: D017785:Photons; D017510:Protein Folding; D011506:Proteins / Q000737:chemistry*; D012235:Rhodamines / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D014364:Tryptophan / Q000032:analysis* / Q000737:chemistry*
chemical_list: D011506:Proteins; D012235:Rhodamines; D014364:Tryptophan; C029773:rhodamine B