Polypeptide Structure and Stability

On the structural side of the Gellman lab, we have been working to elucidate the atomic structures of a-helical, single-pass transmembrane domains using a technique called racemic crystallography. Proteins and peptides are chiral, they consist of amino acids which are chiral (with the exception of glycine) and an additional chirality is observed in a-helical structures, right or left-handedness. This chirality is important to consider when conducting crystallographic studies as chiral molecules can only occupy chiral space groups (65 out of the 230 total space groups). Racemic crystallography was developed in order to allow for proteins and peptides to occupy both chiral and achiral space groups in hopes that targets whose structures were unable to be determined using traditional techniques could be elucidated given a higher number of possible space groups. This technique requires the synthesis of both the L-amino acid and D-amino acid containing versions of the target. When these enantiomers are incubated together, mirror symmetry and inversion symmetry, which are forbidden in the case of chiral molecules, can be observed and this racemic mixture can occupy both achiral and chiral space groups.

We are particularly interested in single-pass transmembrane domains because (1) of their biological relevance (20-30% of the genes in the human genome encode for membrane proteins), (2) they are synthetically tractable, typically around 25 residues in length and (3) transmembrane domains are notoriously difficult to crystallize using traditional crystallization techniques due to their hydrophobic nature. Most recently these efforts have been directed toward the Influenza M2 transmembrane domain and the observed heterochiral dimer interactions (shown left) in these structures have the potential to inform additional studies into heterochiral coiled coil interactions


Recent Publications:

7.  "Effects of Single α-to-β Residue Replacements on Structure and Stability in a Small Protein: Insights from Quasiracemic Crystallization." Kreitler, D.F.; Mortenson, D.E.; Forest, K.F.; Gellman, S.H. J. Am. Chem. Soc. 2016, 138, 6498.

6.  "High-resolution structures of a heterochiral coiled-coil." Mortenson, D.E.; Steinkruger, J.D.; Kreitler, D.F.; Perroni, D.V.; Sorenson, G.P.; Huang, L.; Mittal, R.; Yun ,H.G.; Travis, B.R.; Mahanthappa, M.K.; Forest, K.T.; Gellman, S.H. Proc. Natl. Acad. Sci. U.S.A. 2015, 112, 13144.

5. "Quasiracemate Crystal Structures of Magainin 2 Derivatives Support the Functional Significance of the Phenylalanine Zipper Motif." Hayouka, Z.; Thomas, N.C.; Mortenson, D.E.; Satyshur, K.A.; Weisblum, B.; Forest, K.T.; Gellman, S.H. J. Am. Chem. Soc. 2015, 137, 11884.

4. “Evidence for small-molecule-mediated loop stabilization in the structure of the isolated Pin1 WW domain.” Mortenson DE, Kreitler DF, Yun HG, Gellman SH, Forest KT. Acta Crystallogr. D Biol. Crystallogr. 2013, 2506.

3. "Evidence for Phenylalanine Zipper-Mediated Dimerization in the X-ray Crystal Structure of a Magainin 2 Analogue" Hayouka Z, Mortenson DE, Kreitler DF, Weisblum B, Forest KT,Gellman SH, J. Am. Chem. Soc. 2013, 135, 15738.

2. “Quasiracemic crystallization as a tool to assess the accommodation of noncanonical residues in nativelike protein conformations.”, Mortenson, D.E.; Satyshur, K.A.; Guzei, I.A.; Forest, K.T.; Gellman, S.H., J Am Chem Soc. 2012, 134, 2473-2476.

1. "Maltose-neopentyl glycol (MNG) amphiphiles for solubilization, stabilization and crystallization of membrane proteins",Chae, P. S.; Rasmussen,S. G.; Rana,R. R.; Gotfryd,K.; Chandra,R.; Goren,M. A.; Kruse,A. C.; Nurva,S.; Loland,C. J.; Pierre,Y.; Drew,D.; Popot,J. L.; Picot,D.; Fox,B. G.; Guan,L.; Gether,U.; Byrne,B.; Kobilka, B. and Gellman,S. H. Nat.Methods. 2010, 7,1003-1008.