4.16
Desnaturalización de proteínas
La función de las proteínas depende de su estructura tridimensional nativa, que está dictada por la secuencia de aminoácidos de la proteína específica…
Una proteína solo puede llevar a cabo su actividad biológica en su conformación nativa en condiciones óptimas.
La exposición a ciertos productos químicos o metales pesados, o los cambios en el pH o la temperatura pueden desnaturalizar la proteína, es decir, alterar su estructura tridimensional y hacerla biológicamente inactiva.
Durante la desnaturalización, las interacciones covalentes y no covalentes que mantienen unidas las estructuras terciarias y secundarias de la proteína se rompen, lo que lleva al desenrollamiento de las hélices, la desestabilización de las láminas beta o incluso el despliegue completo de la proteína en su cadena polipeptídica primaria.
En algunos casos, cuando se restablecen las condiciones óptimas, la proteína desnaturalizada puede volver a su forma funcional a través de un proceso llamado renaturalización.
Por ejemplo, cuando el pH de la sangre cae por debajo de 7,35, el exceso de iones H+ se une a la hemoglobina, induciendo cambios conformacionales en su estructura. Estos cambios estructurales impiden que la hemoglobina se una y transporte oxígeno.
Sin embargo, cuando se restablece el pH normal de la sangre, la hemoglobina libera los iones H+ adjuntos, vuelve a adquirir su forma biológicamente activa y reanuda el transporte de oxígeno.
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Q1: What happens to a protein's structure during denaturation?
During denaturation, the covalent and non-covalent interactions holding the protein's tertiary and secondary structures break apart. This causes helices to uncoil, beta sheets to destabilize, and the polypeptide chain to unfold completely. The protein loses its three-dimensional shape and becomes biologically inactive, unable to perform its normal functions.
Q2: How does heat cause protein denaturation?
Heat increases the kinetic energy of molecules, causing them to vibrate vigorously. This vigorous motion disrupts the primary non-covalent interactions, including hydrogen bonds, electrostatic forces, and van der Waals interactions that stabilize the protein's native conformation. As these interactions break down, the protein's three-dimensional structure collapses, leading to denaturation. For example, albumin in eggs coagulates when boiled.
Q3: Why do heavy metals denature proteins?
Heavy metals such as arsenic, mercury, cadmium, chromium, and lead denature proteins by either displacing essential metal ions in metalloproteins or forming complexes with functional side chains. These interactions induce conformational changes in the protein's native structure, hampering its biological activity. For instance, cadmium can replace calcium or zinc ions in metalloproteins, disrupting their function.
Q4: How does ethyl alcohol denature proteins?
Ethyl alcohol disrupts the side chain intramolecular hydrogen bonds within proteins and forms new hydrogen bonds with the protein side chains instead. This disruption affects the protein's tertiary structure, causing the polypeptide chain to unfold and the protein to denature. This denaturing property makes alcohol effective in sanitizers and disinfectants.
Q5: Can denatured proteins regain their function?
Yes, in some cases denatured proteins can refold into their functional form through renaturation when optimal conditions are restored. For example, when blood pH falls below 7.35, hemoglobin denatures and cannot transport oxygen. However, when normal blood pH is restored, hemoglobin releases excess H+ ions, reacquires its biologically active form, and resumes oxygen transport.
Q6: What environmental factors can denature proteins?
Proteins denature when exposed to unfavorable environmental conditions including significant changes in pH or temperature, certain organic compounds, salts, and heavy metals. These factors disrupt the chemical and physical environment that normally favors the protein's folded conformation. The presence of any of these denaturants can spontaneously destabilize the protein's three-dimensional structure.
Q7: Why is a protein's native conformation essential for its biological activity?
A protein can only carry out its biological activity in its native conformation under optimal conditions. The three-dimensional structure is dictated by the amino acid sequence and determines how the protein interacts with other molecules and performs its specific function. Understanding protein denaturation is central to the role of proteins in the human body and how environmental stressors affect their performance.