Pressure as a denaturing agent in studies of single-point mutants of an amyloidogenic protein human cystatin c

The influence of glycation on a high pressure denaturation of ubiquitin

The combination of deuterium–hydrogen exchange (DHX) and mass spectrometry (MS) can be used for studying a high pressure denaturation (HPD) of proteins. Herein we present the results of investigations of the influence of glycation on the HPD of ubiquitin. Application of various values of pressure causes different degrees of protein unfolding, resulting in molecules with a different number of protons available for exchange with deuterons. The dependence of this number on pressure gives information on the denaturation state of a protein. On the basis of the obtained results we can conclude that increasing number of fructosamine moieties in ubiquitin decreases the pressure required for its denaturation. It suggests that glycation moderately decreases the protein stability. The present study is the first example of application of hydrogen–deuterium exchange as a method of investigating the influence of posttranslational modification of protein on the HPD.

The Folding process of Human Profilin-1, a novel protein associated with familial amyotrophic lateral sclerosis

Human profilin-1 is a novel protein associated with a recently discovered form of familial amyotrophic lateral sclerosis. This urges the characterization of possible conformational states, different from the fully folded state, potentially able to initiate self-assembly. Under native conditions, profilin-1 is monomeric and possesses a well-defined secondary and tertiary structure. When incubated at low pH or with high urea concentrations, profilin-1 remains monomeric but populates unfolded states exhibiting larger hydrodynamic radius and disordered structure, as assessed by dynamic light scattering, far-UV circular dichroism and intrinsic fluorescence. Refolding from the urea-unfolded state was studied at equilibrium and in real-time using a stopped-flow apparatus. The results obtained with intrinsic fluorescence and circular dichroism indicate a single phase without significant changes of the corresponding signals before the major refolding transition. However, such a transition is preceded by a burst phase with an observed increase of ANS fluorescence, which indicates the conversion into a transiently populated collapsed state possessing solvent-exposed hydrophobic clusters. Kinetic analysis reveals that such state has a conformational stability comparable to that of the fully unfolded state. To our knowledge, profilin-1 is the first example of an amyloid-related protein where folding occurs in the absence of thermodynamically stable partially folded states.

Nonenzymatic modification of Ubiquitin under high-pressure and -temperature treatment: mass spectrometric studies

The effect of high-pressure and/or high-temperature on the glycation of a model protein (ubiquitin) was investigated by mass spectrometry. This paper reports the impact of high pressure (up to 1200 MPa) on the modification of a ubiquitin using ESI-MS measurements. The application of glucose labeled with stable isotope allows a quantitative assessment of modification under the conditions of high-pressure (HPG) and high-temperature (HTG) glycation. A higher degree of modification was observed for the sample heated at 80 °C for 25 min under atmospheric pressure than for sample treated under high pressure. In samples treated at pressure below 400 MPa an insignificant increase of glycation level was observed, whereas high pressure (>600 MPa) has only a minor effect on the number of hexose moieties (Fru) attached to the lysine residue side chain.

Structural characterization of V57D and V57P mutants of human cystatin C, an amyloidogenic protein

Wild-type human cystatin C (hCC wt) is a low-molecular-mass protein (120 amino-acid residues, 13,343 Da) that is found in all nucleated cells. Physiologically, it functions as a potent regulator of cysteine protease activity. While the biologically active hCC wt is a monomeric protein, all crystallization efforts to date have resulted in a three-dimensional domain-swapped dimeric structure. In the recently published structure of a mutated hCC, the monomeric fold was preserved by a stabilization of the conformationally constrained loop L1 caused by a single amino-acid substitution: Val57Asn. Additional hCC mutants were obtained in order to elucidate the relationship between the stability of the L1 loop and the propensity of human cystatin C to dimerize. In one mutant Val57 was substituted by an aspartic acid residue, which is favoured in β-turns, and in the second mutant proline, a residue known for broadening turns, was substituted for the same Val57. Here, 2.26 and 3.0 Å resolution crystal structures of the V57D andV57P mutants of hCC are reported and their dimeric architecture is discussed in terms of the stabilization and destabilization effects of the introduced mutations.