Question

Similar arrangements of secondary structural motifs are often observed in the fold structure of protein domains. Which of the following is correct? A. Superfolds are similar structures from proteins related by function or evolution from the same primordial gene. B. Folds must be either all \(\alpha\) or all \(\beta\) C. There is only one type of \(\beta\) domain. D. If a protein has more than one domain, all domains are identical. E. A common fold has a central \(\beta\) -barrel with the strands connected by \(\alpha\) -helices around the outside.

Short answer

Answer: A common fold has a central β-barrel with the strands connected by α-helices around the outside.

Step-by-step solution

Option A: Superfolds

Superfolds are characterized by a common structural pattern shared among a diverse group of proteins, even if these proteins don't have a common function or evolutionary history. This statement is partially true, as superfolds share similar structures, but their relatedness may not be solely linked to function or evolution from the same primordial gene.

Option B: Folds Classification

This statement implies that folds must be either all alpha-helices or all beta-strands. However, proteins can have mixed arrangements of secondary structures, so this option is incorrect.

Option C: Beta Domains

This statement suggests that there is only one type of beta domain. However, there are various types of \(\beta\) domains and arrangements in protein structure, so this statement is incorrect.

Option D: Domains within a Protein

This statement claims that if a protein has more than one domain, all domains are identical. However, this is not true since proteins can have different domains that contribute to their unique functions. So, this statement is incorrect.

Option E: Central Beta-Barrel and Alpha-Helices

This statement proposes that a common fold has a central \(\beta\)-barrel with strands connected by \(\alpha\)-helices around the outside. This arrangement is known as the "\(\alpha\)/\(\beta\) barrel" motif, which is found in many enzymes and is a commonly observed fold. This statement is accurate and is the correct answer. So, the correct answer is: E. A common fold has a central \(\beta\)-barrel with the strands connected by \(\alpha\)-helices around the outside.