Final answer:
HSP-70 and HSP-90 both function as chaperone proteins but do not necessarily share a high sequence homology. They are characterized by the presence of HUP domains related to their ATPase activity and are involved in protein folding within cells, particularly under stress conditions.
Step-by-step explanation:
When looking at similarities between HSP-70 and HSP-90, it is important to consider that protein domains are the aspects of proteins that may be conserved across different protein families. The domains within these proteins are responsible for chaperone activity, and they share similar functions related to assisting the correct folding of other proteins and responding to stress conditions.
While the question prompts a specific comparison of sequence between HSP-70 and HSP-90, it should be noted that although both are heat shock proteins and share some level of functional similarity, they do not necessarily have a high degree of sequence homology. Rather, they tend to share a common domain structure used for their chaperone activity, known as the HUP domain. In terms of evolutionary biology, this domain is characterized by certain conserved features such as a particular order of beta-strand sheets and helices, motifs for nucleotide binding, and possible nucleotidyl transferase activity, which might be present in the evolutionary history of these proteins.
Both HSP-70 and HSP-90 exhibit the chaperone-like activity and deal with the unfolding and refolding of other proteins, crucial for cellular homeostasis, especially under stress conditions. The HUP domain class is linked to their biological functions of binding and hydrolyzing ATP, which provides the energy necessary for their chaperone functions.