A Deuterium Nuclear Magnetic Resonance Study of Amino Acid Dynamics in the Membrane Protein, Bacteriorhodopsin (Nmr)

Smith, Rebecca Luann

Permalink

https://hdl.handle.net/2142/70284 Copy

Description

Title

A Deuterium Nuclear Magnetic Resonance Study of Amino Acid Dynamics in the Membrane Protein, Bacteriorhodopsin (Nmr)

Author(s)

Smith, Rebecca Luann

Issue Date

1984

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Chemistry, Physical

Abstract

We have obtained deuterium (('2)H) Fourier transform nuclear magnetic resonance (NMR) spectra for many polycrystalline, deuterium-labelled amino acids in the solid state and where possible, have biosynthetically incorporated them into the membrane protein, bacteriorhodopsin in the photosynthetic purple membrane of Halobacterium halobium. For L{(beta)-('2)H(,3)} alanine, DL{(gamma)-('2)H(,6)} valine, DL{(beta),(gamma)-('2)H(,4)} threonine, L{(delta)-('2)H(,3)} leucine, L{(alpha),(beta),(gamma),(gamma)',(delta)-('2)H(,10)} isoleucine, L{(epsilon)-('2)H(,3)} methionine and {S-methyl-('2)H(,3)} methionine we have obtained deuterio-methyl group spin lattice relaxation times (T(,1)) as a function of temperature. The results yield the Arrhenius activation energies ((DELTA)E('(DBLDAG))) for methyl rotation, and through the use of a suitable mathematical model, rotation correlation time s, (tau)(,c). For L{(beta)-('2)H(,3)} alanine in the zwitterionic lattice, a T(,1) minimum of 2.1 ms is observed at 0(DEGREES)C in excellent agreement with the 1.92 ms prediction of the model. We have also obtained ('2)H NMR spectra and T(,1)'s for L{(delta)(,1),(delta)(,2),(epsilon)(,1),(epsilon)(,2),(zeta)-('2)H(,5)} phenylalanine in the zwitterionic form and incorporated into purple membrane as a function of temperature. The T(,1) results are analyzed using a mathematical model for two-fold flipping about the C(,2) axis. For L{('2)H(,5)} phenylalanine at -30(DEGREES)C in good agreement with the 5 ms prediction of the mathematical model. In methionine, alanine and phenylalanine we see crystal lattice effects on the mobility of the sidechain. Similar sidechain mobility, (tau) and (DELTA)E('(DBLDAG)) measurements are reported for these amino acid sidechains within bacteriorhodopsin. Overall, our results demonstrate a similarity between the dynamics in amino acid crystals and in membrane proteins. We have also identified highly mobile residues on the surface of the membrane bilayer. The mobility of these surface residues is highly effected by trypsin digestion, cross-linking with a carbodiimido and lyopholization of the purple membrane sample.

Graduation Semester

1984

Type of Resource

text

Permalink

http://hdl.handle.net/2142/70284

Owning Collections