Final answer:
The most likely candidate for a transmembrane ß-strand in a ß-barrel protein is sequence (b), which contains a higher proportion of hydrophobic amino acids suitable for integration into the lipid bilayer of the membrane, compared to the other options provided.
Step-by-step explanation:
The most likely candidate for a transmembrane ß-strand in a ß-barrel protein among the given amino acid sequences is (b) Ala-Phe-Leu-Val-Leu-Asp-Lye-Ser-Glu-Thr. This sequence is rich in hydrophobic amino acids, such as alanine (Ala), phenylalanine (Phe), leucine (Leu), and valine (Val) which are compatible with the lipid bilayer's hydrophobic nature.
These nonpolar amino acids would favorably interact with the fatty acid tails within the membrane. Additionally, the sequence contains fewer hydrophilic or charged amino acids, which are generally found facing the aqueous environment inside the pore or outside the cell, and not within the hydrophobic core of the membrane.
In contrast, sequences (a) and (c) contain more charged or polar amino acids like aspartic acid (Asp), lysine (Lys), and glutamic acid (Glu), which are less likely to be found in the hydrophobic regions of a membrane-spanning segment. The presence of these charged amino acids would disrupt the protein's ability to integrate stably into the hydrophobic environment of the lipid bilayer. Sequence (d) does not follow the pattern of alternating hydrophobic and hydrophilic residues as typically seen in ß-barrels and is also less likely due to similar reasons as (a) and (c).