Protein Denaturation and Folding: - Loss of Protein Structure Results in Loss of Function

Protein structures have evolved to function in particular cellular environments. Conditions different from those in the cell can result in protein structural changes, large and small. A loss of three-dimensional structure sufficient to cause loss of function is called denaturation. The denatured state does not necessarily equate with complete unfolding of the protein and randomization of conformation. Under most conditions, denatured proteins exist in a set of partially folded states that are poorly understood. Most proteins can be denatured by heat, which affects the weak interactions in a protein (primarily hydrogen bonds) in a complex manner. If the temperature is increased slowly, a protein’s conformation generally remains intact until an abrupt loss of structure (and function) occurs over a narrow temperature range (Fig. 4–26). The abruptness of the change suggests that un folding is a cooperative process: loss of structure in one part of the protein destabilizes other parts. The effects of heat on proteins are not readily predictable. The very heat-stable proteins of thermophilic bacteria have evolved to function at the temperature of hot springs (~100 C). Yet the structures of these proteins often differ only slightly from those of homologous proteins de rived from bacteria such as Escherichia coli. How these small differences promote structural stability at high temperatures is not yet understood. Proteins can be denatured not only by heat but by extremes of pH, by certain miscible organic solvents such as alcohol or acetone, by certain solutes such as urea and guanidine hydrochloride, or by detergents. Each of these denaturing agents represents a relatively mild treatment in the sense that no covalent bonds in the polypeptide chain are broken. Organic solvents, urea, and detergents act primarily by disrupting the hydrophobic interactions that make up the stable core of globular proteins; extremes of pH alter the net charge on the protein, causing electrostatic repulsion and the disruption of some hydrogen bonding. The denatured states obtained with these various treatments need not be equivalent.

FIGURE 4–26 Protein denaturation. Results are shown for proteins de natured by two different environmental changes. In each case, the transition from the folded to unfolded state is fairly abrupt, suggesting co operativity in the unfolding process. (a) Thermal denaturation of horse apomyoglobin (myoglobin without the heme prosthetic group) and ribonuclease A (with its disulfide bonds intact; see Fig. 4–27). The midpoint of the temperature range over which denaturation occurs is called the melting temperature, or Tm. The denaturation of apo myoglobin was monitored by circular dichroism, a technique that measures the amount of helical structure in a macromolecule. Denaturation of ribonuclease A was tracked by monitoring changes in the intrinsic fluorescence of the protein, which is affected by changes in the environment of Trp residues. (b) Denaturation of disulfide-intact ribonuclease A by guanidine hydrochloride (GdnHCl), monitored by circular dichroism.

اخر الاخبار

اخبار العتبة العباسية المقدسة

مؤسّسة الوافي تُهدي مكتبةَ مسجد الكوفة نسخةً من موسوعة فتوى الدفاع الكفائي

المجمع العلمي يقيم برنامج (سراج المنتظرين) في محافظة المثنى

قسم الشؤون الفكرية ينظم ندوة فكرية عن أبعاد نهضة الإمام الصادق (عليه السلام)

العتبة العباسية المقدسة تناقش تكثيف جهودها الإغاثية لدعم الشعبين الإيراني واللبناني

المزيد

الآخبار الصحية

دواء جديد يحمي القلب ويعزز علاج السرطان في آن واحد

سر غذائي بسيط لحماية القلب مع التقدم في العمر

علامات تشير إلى اختلال عمل الغدة الدرقية

السمنة واللقاحات.. دراسة تكشف تأثيراً سلبياً

المزيد

الآخبار التكنلوجية

البعوض في آيسلندا إشارة مبكرة على تحولات بيئية في القطب الشمالي

صاروخ يطلق قمرا اصطناعيا في مدار خاطئ

"أوبن إيه آي" تطلق نموذجا للعلوم الحيوية واكتشاف الأدوية

تفوق على البشر.. روبوت يحطم الرقم القياسي لسباق نصف ماراثون !

المزيد

مواضيع ذات صلة

Complementary Interactions between Proteins and Ligands: The Immune System and Immunoglobulins: -The Immune Response Features a Specialized Array of Cells and Proteins

Reversible Binding of a Protein to a Ligand: Oxygen-Binding Proteins: -Sickle-Cell Anemia Is a Molecular Disease of Hemoglobin

Reversible Binding of a Protein to a Ligand: Oxygen-Binding Proteins: -Oxygen Binding to Hemoglobin Is Regulated by 2,3-Bisphosphoglycerate

Protein Tertiary and Quaternary Structures: -There Are Limits to the Size of Proteins

Protein Tertiary and Quaternary Structures: -Protein Quaternary Structures Range from Simple Dimers to Large Complexes

Reversible Binding of a Protein to a Ligand: Oxygen-Binding Proteins: -Protein-Ligand Interactions Can Be Described Quantitatively

Reversible Binding of a Protein to a Ligand: Oxygen-Binding Proteins:- Myoglobin Has a Single Binding Site for Oxygen

Reversible Binding of a Protein to a Ligand: Oxygen-Binding Proteins:- Oxygen Can Be Bound to a Heme Prosthetic Group

Protein Denaturation and Folding:- Some Proteins Undergo Assisted Folding

Protein Denaturation and Folding:- Polypeptides Fold Rapidly by a Stepwise Process

Protein Denaturation and Folding: - Amino Acid Sequence Determines Tertiary Structure

Protein Tertiary and Quaternary Structures: -Protein Quaternary Structures Range from Simple Dimers to Large Complexes