Question

What form of HSP-90 is used in the ER?

Answer 1

HSP-90 in the ER is specialized for refolding and quality control of newly synthesized proteins, ensuring their correct folding and function in the cell.

Step-by-step explanation:

The form of HSP-90 used in the endoplasmic reticulum (ER) is specialized for its function in that cellular compartment. Heat shock proteins such as HSP-90 are responsible for a variety of cellular processes, including protecting cells against metabolic damage during stress conditions, like heat shock, by refolding misfolded proteins. This protective mechanism is critical as it allows cells to cope with stress by increasing the activity of proteins that assist in the refolding process. HSP-90 in the ER is part of a quality control system for newly synthesized proteins, ensuring correct folding and preventing misfolded proteins from accumulating.

Regarding the biogenesis of proteins destined for organelles such as the mitochondria, HSP70 plays a different chaperone role by assisting the entry of proteins into the mitochondrial matrix. This involves the unfolding and refolding of proteins as they translocate across the mitochondrial membrane. Although HSP70 is important in this context, the specific form of HSP-90 utilized within the ER is distinct and integral to its function there.

Answer 2

In the ER, the distinct form of HSP-90 is known as GRP94, which functions as a molecular chaperone similar to its cytosolic counterparts but is adapted to the unique conditions found within the ER, playing a critical role during stress response mechanisms such as the unfolded protein response.

Step-by-step explanation:

HSP-90 in the Endoplasmic Reticulum

The form of HSP-90 that is used in the endoplasmic reticulum (ER) is structurally and functionally distinct from those in other cellular compartments such as the cytosol. While the canonical HSP-90 proteins function as molecular chaperones to stabilize and fold various client proteins, the ER variant, known as GRP94 (Glucose-Regulated Protein 94), is attuned to the unique environment of the ER. GRP94 shares similar molecular chaperone functions with cytosolic HSP-90 but is specifically involved in the folding and quality control of secretory and membrane proteins within the ER.

GRP94 is particularly important during cellular stress responses, such as the unfolded protein response (UPR) in the ER. This stress response mechanism is essential for maintaining cellular function and homeostasis during conditions that lead to protein misfolding within the ER. The heat shock proteins (HSPs) were first discovered due to their upregulation in response to heat shock, which is now known to include a variety of stress conditions leading to protein damage. GRP94 is a key component in protecting cells from the accumulation of misfolded proteins during times of stress.