Novel Insights into Mercury Effects on Hemoglobin and Membrane Proteins in Human Erythrocytes

Abstract

Mercury (Hg) is a global environmental pollutant that affects human and ecosystem health. With the aim of exploring the Hg-induced protein modifications, intact human erythrocytes were exposed to HgCl2 (1–60 µM) and cytosolic and membrane proteins were analyzed by SDS-PAGE and AU-PAGE. A spectrofluorimetric assay for quantification of Reactive Oxygen Species (ROS) generation was also performed. Hg2+ exposure induces alterations in the electrophoretic profile of cytosolic proteins with a significant decrease in the intensity of the hemoglobin monomer, associated with the appearance of a 64 kDa band, identified as a mercurized tetrameric form. This protein decreases with increasing HgCl2 concentrations and Hg-induced ROS formation. Moreover, it appears resistant to urea denaturation and it is only partially dissociated by exposure to dithiothreitol, likely due to additional protein–Hg interactions involved in aggregate formation. In addition, specific membrane proteins, including band 3 and cytoskeletal proteins 4.1 and 4.2, are affected by Hg2+-treatment. The findings reported provide new insights into the Hg-induced possible detrimental effects on erythrocyte physiology, mainly related to alterations in the oxygen binding capacity of hemoglobin as well as decreases in band 3-mediated anion exchange. Finally, modifications of cytoskeletal proteins 4.1 and 4.2 could contribute to the previously reported alteration in cell morphology.

New Insights into Alterations in PL Proteins Affecting Their Binding to DNA after Exposure of Mytilus galloprovincialis to Mercury—A Possible Risk to Sperm Chromatin Structure?

“…That HgCl 2 induces protein aggregation has already been reported for other proteins. For example, Arnhold et al 2015 [ 34 ] identified amyloid protein aggregation in the cell nucleus as a novel Hg–bio-interaction pathway [ 34 ], and we, in our previous studies, showed the formation of a mercerized tetrameric Hb as a result of treating human erythrocytes with increasing concentrations of HgCl 2 [ 5 ]. We also investigated the possibility of mercury-induced conformational changes in PL proteins using fluorescence spectroscopy.…”

“…Although heavy metals are generally present in trace amounts in natural waters, a large number of them are toxic even at very low concentrations [ 1 ], posing a serious danger to marine organisms [ 2 , 3 , 4 ]. Among the various heavy metals, mercury (Hg) has drawn a lot of attention, as it is the most toxic nonessential metal [ 5 ]. Mercury has captured the attention of the scientific community since the 1950s, when the first evidence of hazardous environmental impacts were reported [ 6 ], which led to policies and regulations to limit Hg emissions.…”

Spermatozoa Transcriptional Response and Alterations in PL Proteins Properties after Exposure of Mytilus galloprovincialis to Mercury

“…In the life cycle of bivalves, the early developmental stages result in being most susceptible to various pollutants, such as toxic metals [ 8 ], pesticides [ 9 ], and antifouling paints [ 10 ], and it has been demonstrated that the concentrations of toxic metals able to cause lethal toxicity in embryos and larvae are much lower than those that are lethal to adults [ 11 , 12 ]. Among toxic metals, mercury (Hg) is one of the most toxic nonessential metals [ 13 ]. Mercury contamination in seawater is an issue to the environment and human health.…”

Erythrocytes as a Model for Heavy Metal-Related Vascular Dysfunction: The Protective Effect of Dietary Components

“…In particular, Hg inhibitory activity on the glycolytic enzymes hexokinase and phosphofructokinase has been reported [ 53 ]. Also, membrane proteins are modified by Hg, including tubulin [ 54 ] and erythrocyte (RBC) band 3 and 4.1 and 4.2 proteins [ 55 ].…”

“…It is important to emphasise that the reported Hg-induced damage to hemoglobin (Hb) may also contribute to the decreased bioavailability of this key vasorelaxant molecule [ 130 , 131 ]. A tetrameric mercurized form of Hb, supposed to be dysfunctional in physiological conformational changes crucial for the oxygenation/deoxygenation process, can be observed after RBC exposure to Hg 2+ [ 55 ]. As discussed in the introduction, accessible Cys residues represent the preferential site of Hg–protein interaction.…”