N-acylation of cytosolic proteins is a common occurrence in tissues, and it regulates protein structure and function. The major N-acylation types in cells are acetylation, propionylation, succinylation and malonylation, which are initiated by the enzymatic or non-enzymatic transfer of acetyl CoA, propionyl CoA, succinyl CoA and malonyl CoA to lysine residues, respectively. Lens proteins are long lived with little or no turnover, and thus, post-translational modifications (PTMs) accumulate with age. The lack of enzymatically active proteins, particularly in the core of the lens, prohibits the reversal of PTMs. Thus, if deacylases are weak in the lens, acylation is mostly a one-way reaction that leads to permanent modifications of lens proteins, which appears to be the case (based on our preliminary data). The effects of acylation on lens proteins remain largely unknown. As shown in our previous study, the acetylation makes ?-crystallin a better chaperone. In addition, our preliminary data show that lens proteins are also propionylated, succinylated and malonylated and that acetylation and succinylation increase the thermal stability and solubility of the proteins. Thus, we hypothesize that acylation of lens proteins is a beneficial PTM that helps maintain the chaperone activity of ?- crystallin as well as the stability and solubility of lens proteins during aging. We will test this hypothesis in three aims.
In Aim 1, we will determine the major acylation sites in human lens ?-crystallin by mass spectrometric analyses and determine the effect of age on these modifications.
In Aim 2, we will determine effects of acylation on the structure and function of ?-crystallin.
In Aim 3, we will evaluate the effects of acylation on the stability and solubility of lens proteins and determine whether acylation can be used to improve the compromised resilience of aged human lenses.
Presbyopia, or the loss of lens accommodation, and cataracts are the leading causes of vision impairment and blindness worldwide. Therapies are not available to prevent either of these maladies. Acylation of lens protein, a chemical reaction between lysine residues in lens proteins and acyl CoA metabolites in the lens, makes ?-crystallin a better chaperone protein, and more interestingly, increases protein solubility in aged lenses. This intriguing observation provides us an opportunity to investigate lens protein acylation more thoroughly, and the findings may help us develop therapies to prevent presbyopia and cataract formation.