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Low microwave-amplitude ESR spectroscopy: Measuring spin-relaxation interactions of moderately immobilized spin labels in proteins
KTH, Tidigare Institutioner, Bioteknologi.
KTH, Tidigare Institutioner, Biokemi och biokemisk teknologi.
2004 (engelsk)Inngår i: Journal of Biochemical and Biophysical Methods, ISSN 0165-022X, E-ISSN 1872-857X, Vol. 60, nr 2, s. 117-138Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

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 (h(1) < 0.36 G) only requires standard, commercially available ESR equipment. The effect of relaxation enhancement on the spin-spin-relaxation time, T-2e, 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-Delta(3)-pyrroline-3-methyl)methanethiosulfonate (MTSL), and a spin-labeled protein (Thermomyces lanuginosa lipase, TLL-1252C), 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.

sted, utgiver, år, opplag, sider
2004. Vol. 60, nr 2, s. 117-138
Emneord [en]
electron spin resonance, microwave saturation, MTSL, crox, lipase, electron-paramagnetic-resonance, thermomyces-lanuginosa lipase, bacteriorhodopsin mutants, progressive saturation, membrane transporter, linewidth analysis, loop region, dynamics, liquids, conformation
HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-23667DOI: 10.1016/j.jbbm.2004.05.002ISI: 000223463400003Scopus ID: 2-s2.0-3242710304OAI: oai:DiVA.org:kth-23667DiVA, id: diva2:342366
Merknad
QC 20100525 QC 20110923Tilgjengelig fra: 2010-08-10 Laget: 2010-08-10 Sist oppdatert: 2017-12-12bibliografisk kontrollert
Inngår i avhandling
1. Lipase-Lipid Interactions Studied by Site-Directed Labeling and Biological Spectroscopy
Åpne denne publikasjonen i ny fane eller vindu >>Lipase-Lipid Interactions Studied by Site-Directed Labeling and Biological Spectroscopy
2006 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

This thesis describes the study of lipase–lipid interactions of the triglyceride lipase Thermomyces lanuginosus lipase, TLL, by use of site-directed chemical labeling and biological spectroscopy. Several single-cysteine variants of TLL were produced, and labeled with probes containing either an affinity-, a fluorescence- or a spin-label functionality. A combined reduction- and labeling protocol was elaborated for the TLL single-cysteine variants, which were found to be prematurely oxidized during production. A diagnostic dot-blot method based on biotin-avidin interactions was established for the detection of free thiols in recombinant proteins. This method has a picomole detection limit and was found accurate in free thiol quantitation.

Unilamellar phospholipid vesicles consisting of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol (POPG) or of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidyl-choline (POPC) were produced as stable, well-defined lipid interfaces, to which TLL is known to bind with high affinity. The binding orientation of TLL was investigated, employing eleven spin-labeled TLL single-cysteine variants with the point-mutations positioned around the protein surface. Spin-relaxation enhancement was induced by the spin-relaxation agent chromium(III) oxalate (Crox), and a novel ESR-method for measuring the interactions of nitroxide spin-labels at low-microwave amplitudes was established. This method requires only standard ESR-instrumentation and is optimal for surface-exposed spin-labels. The interactions of TLL spin-labels with Crox in the aqueous phase were studied by ESR spectroscopy, while spin-label interactions with the lipid phase were analyzed by fluorescence quenching of dansyl-labeled vesicles. In addition, ESR-data was employed in conjunction with electrostatic potential-based modeling to dock TLL on the membrane of small POPG vesicles. This afforded information on the detailed molecular orientation of TLL at the lipid–water interface.

TLL was found to bind on 50-nm–diameter POPG vesicles in an activated form with the active-site entrance and the proximal part of the lid oriented against the lipid membrane. On 100 nm POPG vesicles and 50 nm POPC vesicles, TLL was oriented with the active site facing away from the membrane, corresponding to approximately a 180-degree–rotation about TLL’s vertical axis. There was no deep penetration of TLL residues in the lipid membranes, but TLL was found to associate closer to the negatively charged POPG-surface, than that of the zwitterionic POPC. TLL was also able to bind to two vesicles simultaneously, as revealed by fluorescence resonance energy transfer (FRET) between fluorescent labeled vesicles. The experimental data obtained provided insights into the interfacial behaviour of a triglyceride lipase.

sted, utgiver, år, opplag, sider
Stockholm: KTH, 2006. s. x, 68
Emneord
thermomyces lanuginous lipase, site-directed labeling, lipase-lipid interactions
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-618 (URN)91-7178-253-2 (ISBN)
Disputas
2006-02-24, Svedbergssalen, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00
Opponent
Veileder
Merknad
QC 20100830Tilgjengelig fra: 2006-02-10 Laget: 2006-02-10 Sist oppdatert: 2010-08-30bibliografisk kontrollert

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