These two effects are mainly responsible for cataract. In addition, some PTMs absorb light in the visible spectral range thereby reducing lens transparency and giving rise to coloration. The absence of protein turnover brings about the accumulation of a large number of PTMs in crystallins, resulting in protein misfolding and aggregation 8, which in turn increases light scattering. This means that protein synthesis is impossible and therefore the proteins synthesised in new cells remain in mature cells for their entire lifespan. The absence of organelles gives the eye lens optical homogeneity and minimises Rayleigh scattering. Matured eye lens fibre cells do not contain organelles apart from the proteasome 7. The eye lens grows layer by layer throughout the lifespan of the organism. It might be also used for in vitro or ex vivo drug screening applications and for monitoring changes in the lens structure in the course of administration of cataract cure medications. Hence, monitoring the formation of PTMs in crystallins has the potential to elevate cataract diagnostics to the molecular level and develop a more sensitive method applicable in the latent phase of the disorder, as well as providing a mechanistic insight into cataractogenesis. However the formation of micron-size defects is preceded, and likely to be caused, by the formation of multiple PTMs in the eye lens crystallin proteins 3, 4, 5, 6. The aging population inevitably increases the number of people with cataract and hence the number of required operations.Ĭurrent cataract diagnosis is based on light scattering methods 2 which can detect defects in the lens structure when they become comparable or greater than the optical wavelength, i.e. Currently the only treatment available for cataract is surgery. According to the assessment of the World Health Organisation (WHO) cataract was responsible for 51% of the world blindness, which represented about 20 million people in 2010 1. Similar content being viewed by othersĬataract remains the leading cause of blindness in both developed and developing countries. We show that the cumulative fraction of OH-Trp, NFK and ArgP emission dominates the total fluorescence spectrum in both emulsified post-surgical human cataract protein samples, as well as in whole lenses and that this correlates strongly with cataract grade and age. Fluorescence of Trp, its derivatives and argpyrimidine (ArgP) can be excited at the red edge of the Trp absorption band which allows normalisation of the emission spectra of these PTMs to the fluorescence intensity of Trp, to determine semi-quantitatively their concentration.

Notably, the lifetime constants of these residues in a model peptide were considerably greater than those of their “free” counterparts.

Significant differences between fluorescence lifetimes of “free” Trp derivatives hydroxytryptophan (OH-Trp), N-formylkynurenine (NFK), kynurenine (Kyn), hydroxykynurenine (OH-Kyn) and their residues were observed. Fluorescence intensity profiles measured along the optical axis of human eye lenses with age-related nuclear cataract showed increasing concentration of fluorescent PTM towards the lens centre in accord with the increased optical density in the lens nucleolus. The chemical nature of the non-tryptophan (non-Trp) fluorescence of porcine and human eye lens proteins was identified by Mass Spectrometry (MS) and Fluorescence Steady-State and Lifetime spectroscopy as post-translational modifications (PTM) of Trp and Arg amino acid residues.

Chaperone proteins eye cataract