Answer;
-Structural protein
Explanation;
Arrow A is indicating a structural protein. (refer to the attached photo)
Structural proteins are the most abundant class of proteins in nature. Collagen is recognized as the most abundant mammalian protein. Structural proteins such as collagen, fibronectin and laminin are utilized in cell culture applications as attachment factors.
-Structural proteins maintain cell shape, akin to a skeleton, and they compose structural elements in connective tissues like cartilage and bone in vertebrates.