Disulfide bonds are unique among post-translational modifications, as they add covalent crosslink... more Disulfide bonds are unique among post-translational modifications, as they add covalent crosslinks to the polypeptide chain. Accordingly, they can exert pronounced effects on protein folding and stability. This is of particular importance for secreted or cell surface proteins, where disulfide bonds are abundant and serve to stabilize proteins against unfolding and dissociation in the extracellular milieu. However, in addition to these bonds providing security to a natively folded protein or aiding the folding process by stabilizing folding intermediates, the cysteines that form these bonds can be perilous during the maturation of nascent polypeptide chains as they enter the endoplasmic reticulum where the concentration of unfolded proteins approaches millimolar levels. This danger is even greater if the native bonds ultimately form between non-consecutive cysteines that are distant in the linear sequence or if non-native bonds are a prerequisite to achieving the final, functional structure of a protein. A wealth of exquisite detail has been obtained from in vitro studies on the biophysical effects of disulfide bonds on protein folding. Correspondingly, in-depth in vivo studies have established that the same principles apply to oxidative folding in a cell, but reveal a much more complex folding trajectory for many of the proteins that have been examined. In this chapter, we review the biophysical properties of disulfide bonds and how they affect the structure and folding of individual proteins. Based on this, we discuss similarities and differences between in vitro and in vivo folding reactions. The types of disulfide bonds that form during co-translational protein folding are described, as are the cellular strategies for accommodating this risk-laden covalent modification. We conclude with a discussion of the impact of disulfide bonds on protein misfolding and human disease.
Endoplasmic reticulum quality control (ERQC) pathways comprising chaperones, folding enzymes, and... more Endoplasmic reticulum quality control (ERQC) pathways comprising chaperones, folding enzymes, and degradation factors ensure the fidelity of ER protein folding and trafficking to downstream secretory environments. However, multiple factors, including tissue-specific secretory proteomes, environmental and genetic insults, and organismal aging, challenge ERQC. Thus, a key question is: how do cells adapt ERQC to match the diverse, ever-changing demands encountered during normal physiology and in disease? The answer lies in the unfolded protein response (UPR), a signaling mechanism activated by ER stress. In mammals, the UPR comprises three signaling pathways regulated downstream of the ER membrane proteins IRE1, ATF6, and PERK. Upon activation, these UPR pathways remodel ERQC to alleviate cellular stress and restore ER function. Here, we describe how UPR signaling pathways adapt ERQC, highlighting their importance for maintaining ER function across tissues and the potential for targeting the UPR to mitigate pathologies associated with protein misfolding diseases.
Proteins that are expressed on membrane surfaces or secreted are involved in all aspects of cellu... more Proteins that are expressed on membrane surfaces or secreted are involved in all aspects of cellular and organismal life, and as such require extremely high fidelity during their synthesis and maturation. These proteins are synthesized at the endoplasmic reticulum (ER) where a dedicated quality control system (ERQC) ensures only properly matured proteins reach their destinations. An essential component of this process is the identification of proteins that fail to pass ERQC and their retrotranslocation to the cytosol for proteasomal degradation. This study by Wu et al. reports a cryo-electron microscopy (cryo-EM) structure of the five-protein channel through which aberrant proteins are extracted from the ER, providing insights into how recognition of misfolded proteins is coupled to their transport through a hydrophobic channel that acts to thin the ER membrane, further facilitating their dislocation to the cytosol1.
Antibody monomers are produced from two immunoglobulin heavy chains and two light chains that are... more Antibody monomers are produced from two immunoglobulin heavy chains and two light chains that are folded and assembled in the endoplasmic reticulum This process is assisted and monitored by components of the endoplasmic reticulum quality control machinery; an outcome made more fraught by the unusual genetic machinations employed to produce a seemingly unlimited antibody repertoire. Proper functioning of the adaptive immune system is as dependent on the success of this operation, as it is on the ability to identify and degrade those molecules that fail to reach their native state. In this study, two rate-limiting steps were identified in the degradation of a non-secreted κ light chain. Both focus on the constant domain (CL), which has evolved to fold rapidly and very stably to serve as a catalyst for the folding of the heavy chain CH1 domain. The first hurdle is the reduction of the disulfide bond in the CLdomain, which is required for retrotranslocation to the cytosol. In spite of b...
All in-text references underlined in blue are linked to publications on ResearchGate, letting you... more All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately.
Disulfide bonds are unique among post-translational modifications, as they add covalent crosslink... more Disulfide bonds are unique among post-translational modifications, as they add covalent crosslinks to the polypeptide chain. Accordingly, they can exert pronounced effects on protein folding and stability. This is of particular importance for secreted or cell surface proteins, where disulfide bonds are abundant and serve to stabilize proteins against unfolding and dissociation in the extracellular milieu. However, in addition to these bonds providing security to a natively folded protein or aiding the folding process by stabilizing folding intermediates, the cysteines that form these bonds can be perilous during the maturation of nascent polypeptide chains as they enter the endoplasmic reticulum where the concentration of unfolded proteins approaches millimolar levels. This danger is even greater if the native bonds ultimately form between non-consecutive cysteines that are distant in the linear sequence or if non-native bonds are a prerequisite to achieving the final, functional structure of a protein. A wealth of exquisite detail has been obtained from in vitro studies on the biophysical effects of disulfide bonds on protein folding. Correspondingly, in-depth in vivo studies have established that the same principles apply to oxidative folding in a cell, but reveal a much more complex folding trajectory for many of the proteins that have been examined. In this chapter, we review the biophysical properties of disulfide bonds and how they affect the structure and folding of individual proteins. Based on this, we discuss similarities and differences between in vitro and in vivo folding reactions. The types of disulfide bonds that form during co-translational protein folding are described, as are the cellular strategies for accommodating this risk-laden covalent modification. We conclude with a discussion of the impact of disulfide bonds on protein misfolding and human disease.
Endoplasmic reticulum quality control (ERQC) pathways comprising chaperones, folding enzymes, and... more Endoplasmic reticulum quality control (ERQC) pathways comprising chaperones, folding enzymes, and degradation factors ensure the fidelity of ER protein folding and trafficking to downstream secretory environments. However, multiple factors, including tissue-specific secretory proteomes, environmental and genetic insults, and organismal aging, challenge ERQC. Thus, a key question is: how do cells adapt ERQC to match the diverse, ever-changing demands encountered during normal physiology and in disease? The answer lies in the unfolded protein response (UPR), a signaling mechanism activated by ER stress. In mammals, the UPR comprises three signaling pathways regulated downstream of the ER membrane proteins IRE1, ATF6, and PERK. Upon activation, these UPR pathways remodel ERQC to alleviate cellular stress and restore ER function. Here, we describe how UPR signaling pathways adapt ERQC, highlighting their importance for maintaining ER function across tissues and the potential for targeting the UPR to mitigate pathologies associated with protein misfolding diseases.
Proteins that are expressed on membrane surfaces or secreted are involved in all aspects of cellu... more Proteins that are expressed on membrane surfaces or secreted are involved in all aspects of cellular and organismal life, and as such require extremely high fidelity during their synthesis and maturation. These proteins are synthesized at the endoplasmic reticulum (ER) where a dedicated quality control system (ERQC) ensures only properly matured proteins reach their destinations. An essential component of this process is the identification of proteins that fail to pass ERQC and their retrotranslocation to the cytosol for proteasomal degradation. This study by Wu et al. reports a cryo-electron microscopy (cryo-EM) structure of the five-protein channel through which aberrant proteins are extracted from the ER, providing insights into how recognition of misfolded proteins is coupled to their transport through a hydrophobic channel that acts to thin the ER membrane, further facilitating their dislocation to the cytosol1.
Antibody monomers are produced from two immunoglobulin heavy chains and two light chains that are... more Antibody monomers are produced from two immunoglobulin heavy chains and two light chains that are folded and assembled in the endoplasmic reticulum This process is assisted and monitored by components of the endoplasmic reticulum quality control machinery; an outcome made more fraught by the unusual genetic machinations employed to produce a seemingly unlimited antibody repertoire. Proper functioning of the adaptive immune system is as dependent on the success of this operation, as it is on the ability to identify and degrade those molecules that fail to reach their native state. In this study, two rate-limiting steps were identified in the degradation of a non-secreted κ light chain. Both focus on the constant domain (CL), which has evolved to fold rapidly and very stably to serve as a catalyst for the folding of the heavy chain CH1 domain. The first hurdle is the reduction of the disulfide bond in the CLdomain, which is required for retrotranslocation to the cytosol. In spite of b...
All in-text references underlined in blue are linked to publications on ResearchGate, letting you... more All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately.
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