Question

9. (12 points) Spectrin is a cytoskeletal protein that lines the intracellular side of the plasma membrane in eukaryotic cells. Two subunits, spectrin alpha and spectrin beta, will dimerize to form heterodimers; these heterodimers will assemble into hexagonal or pentagonal structures to provide mechanical support for the membrane bilayer. (For this problem, we are primarily interested in the human alpha chain. Make a note of any assumptions if you are unsure of your answer.) a. What is the structural classification/domain assignment of human alpha spectrin? Include your source. b. Show the annotation of secondary structural elements as a function of sequence. Include your source. c. What is the sequence of human alpha spectrin? Include your source. d. Globally align the sequence in 9b with the human beta form of spectrin. How similar are they? Include your alignment and a description of how it was obtained. e. How many 3D structures have been deposited of "spectrin"? Find one that is a near full length human alpha spectrin repeat, list its 4 character identifier code, the method that was used to obtain the structure and the resolution.

Answer 1

Spectrin is a large, cytoskeletal, and heterodimeric protein composed of modular structure of α and β subunits, it typically contains 106 contiguous amino acid sequence motifs called "spectrin repeats". Spectrin is crucial for maintaining the stability and structure of the cell membrane and the shape of a cell. Moreover, it contributes to diverse cell functions such as cell adhesion, cell spreading, and the cell cycle. Mutations of spectrin lead to various human diseases such as hereditary hemolytic anemia, type 5 spinocerebellar ataxia, cancer, as well as others.

actin protein 4.1 tropomyosin B-spectin glycoprotein C A-spectin

Protein secondary structure is the three dimensional form of local segments of proteins. The two most common secondary structural elements are alpha helices and beta sheets, though beta turns and omega loops occur as well. Secondary structure elements typically spontaneously form as an intermediate before the protein folds into its three dimensional tertiary structure.

Secondary structure is formally defined by the pattern of hydrogen bonds between the amino hydrogen and carboxyl oxygen atoms in the peptide backbone. Secondary structure may alternatively be defined based on the regular pattern of backbone dihedral angles in a particular region of the Ramachandran plot regardless of whether it has the correct hydrogen bonds.

The concept of secondary structure was first introduced by Kaj Ulrik Linderstrøm-Lang at Stanford in 1952.