Low microwave-amplitude ESR spectroscopy: Measuring spin-relaxation interactions of moderately immobilized spin labels in proteins

TY - JOUR

T1 - Low microwave-amplitude ESR spectroscopy

T2 - Measuring spin-relaxation interactions of moderately immobilized spin labels in proteins

AU - Hedin, Eva M.K.

AU - Hult, Karl

AU - Mouritsen, Ole G.

AU - Høyrup, Pernille

PY - 2004/8/31

Y1 - 2004/8/31

N2 - Electron spin resonance (ESR) spectroscopy in combination with site-directed spin labeling (SDSL) is a powerful tool for determining protein structure, dynamics and interactions. We report here a method for determining interactions between spin labels and paramagnetic relaxation agents, which is performed under subsaturating conditions. The low microwave-field amplitude employed (h1<0.36 G) only requires standard, commercially available ESR equipment. The effect of relaxation enhancement on the spin-spin-relaxation time, T2e, is measured by this method, and compared to classical progressive power saturation performed on a free spin label, (1-oxyl-2,2,5,5-tetramethyl-Δ3-pyrroline-3-methyl) methanethiosulfonate (MTSL), and a spin-labeled protein (Thermomyces lanuginosa lipase, TLL-I252C), employing the water-soluble relaxation agent chromium(III) oxalate (Crox) in concentrations between 0-10 mM. The low-amplitude theory showed excellent agreement with that of classical power saturation in quantifying Crox-induced relaxation enhancement. Low-amplitude measurements were then performed using a standard resonator, with Crox, on 11 spin-labeled TLL mutants displaying rotational correlation times in the motional narrowing regime. All spin-labeled proteins exhibited significant changes in T 2e. We postulate that this novel method is especially suitable for studying moderately immobilized spin labels, such as those positioned at exposed sites in a protein. This method should prove useful for research groups with access to any ESR instrumentation.

AB - Electron spin resonance (ESR) spectroscopy in combination with site-directed spin labeling (SDSL) is a powerful tool for determining protein structure, dynamics and interactions. We report here a method for determining interactions between spin labels and paramagnetic relaxation agents, which is performed under subsaturating conditions. The low microwave-field amplitude employed (h1<0.36 G) only requires standard, commercially available ESR equipment. The effect of relaxation enhancement on the spin-spin-relaxation time, T2e, is measured by this method, and compared to classical progressive power saturation performed on a free spin label, (1-oxyl-2,2,5,5-tetramethyl-Δ3-pyrroline-3-methyl) methanethiosulfonate (MTSL), and a spin-labeled protein (Thermomyces lanuginosa lipase, TLL-I252C), employing the water-soluble relaxation agent chromium(III) oxalate (Crox) in concentrations between 0-10 mM. The low-amplitude theory showed excellent agreement with that of classical power saturation in quantifying Crox-induced relaxation enhancement. Low-amplitude measurements were then performed using a standard resonator, with Crox, on 11 spin-labeled TLL mutants displaying rotational correlation times in the motional narrowing regime. All spin-labeled proteins exhibited significant changes in T 2e. We postulate that this novel method is especially suitable for studying moderately immobilized spin labels, such as those positioned at exposed sites in a protein. This method should prove useful for research groups with access to any ESR instrumentation.

KW - chromium(III) oxalate

KW - continuous wave

KW - Crox

KW - CW

KW - DL-dithiothreitol

KW - DTT

KW - EDTA

KW - Electron spin resonance

KW - electron spin resonance

KW - electrospray mass spectroscopy

KW - Electrospray MS

KW - ESR

KW - ethylenediamine tetraacetic acid

KW - HEPES

KW - Lipase

KW - Microwave saturation

KW - MTSL

UR - http://www.scopus.com/inward/record.url?scp=3242710304&partnerID=8YFLogxK

U2 - 10.1016/j.jbbm.2004.05.002

DO - 10.1016/j.jbbm.2004.05.002

M3 - Journal article

C2 - 15262447

AN - SCOPUS:3242710304

SN - 0165-022X

VL - 60

SP - 117

EP - 138

JO - Journal of Biochemical and Biophysical Methods

JF - Journal of Biochemical and Biophysical Methods

IS - 2

ER -