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X-ray and neutron scattering studies on some nanoscale structures in molecular biology

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Title: X-ray and neutron scattering studies on some nanoscale structures in molecular biology
Author: Ikonen, Teemu
Contributor: University of Helsinki, Faculty of Science, Department of Physical Sciences, Division of X-ray Physics
Thesis level: Doctoral dissertation (article-based)
Abstract: Scattering of X-rays and neutrons has been applied to the study of nanostructures with interesting biological functions. The systems studied were the protein calmodulin and its complexes, bacterial virus bacteriophage phi6, and the photosynthetic antenna complex from green sulfur bacteria, chlorosome. Information gathered using various structure determination methods has been combined to the low resolution information obtained from solution scattering.

Conformational changes in calmodulin-ligand complex were studied by combining the directional information obtained from residual dipole couplings in nuclear magnetic resonance to the size information obtained from small-angle X-ray scattering from solution.

The locations of non-structural protein components in a model of bacteriophage phi6, based mainly on electron microscopy, were determined by neutron scattering, deuterium labeling and contrast variation.

New data are presented on the structure of the photosynthetic antenna complex of green sulfur bacteria and filamentous anoxygenic phototrophs, also known as the chlorosome. The X-ray scattering and electron cryomicroscopy results from this system are interpreted in the context of a new structural model detailed in the third paper of this dissertation. The model is found to be consistent with the results obtained from various chlorosome containing bacteria. The effect of carotenoid synthesis on the chlorosome structure and self-assembly are studied by carotenoid extraction, biosynthesis inhibition and genetic manipulation of the enzymes involved in carotenoid biosynthesis. Carotenoid composition and content are found to have a marked effect on the structural parameters and morphology of chlorosomes.Työssä on käytetty röntgen- ja neutronisäteilyn sirontaa molekyylibiologian kannalta mielenkiintoisten, nanometrin kokoluokkaan kuuluvien rakenteiden tutkimiseen. Tutkitut systeemit ovat proteiineja, proteiinikomplekseja, viruksia ja vihreiden bakteerien fotosynteesin kannalta tärkeä antennikompleksi, klorosomi.

Erilaisten rakennetutkimusmenetelmien antamaa informaatiota on yhdistetty sirontamenetelmillä saatavaan matalan resoluution rakennetietoon. Ensimmäisessä osajulkaisussa proteiinin konformaatiomuutosta tutkittiin yhdistämällä ydinmagneettisen resonanssin antama suuntatieto röntgensironnasta määritettyyn konformaatiomuutoksen suuruuteen. Toisessa osajulkaisussa määritettiin proteiiniosasten paikka elektronimikroskopian avulla luodussa virusmallissa neutronisironnan ja kontrastivariaation avulla.

Kolmessa viimeisessä osajulkaisussa esitetään uusi malli vihreiden bakteerien fotosynteettisen kompleksin antenniosan rakenteelle ja sen todetaan olevan sopusoinnussa useista eri bakteerilajeista saatujen röntgensironta- ja elektronimikroskopiatulosten kanssa. Karotenoidien vaikutusta rakenteeseen tutkittiin soveltamalla edellä mainittuja menetelmiä bakteereihin, joiden karotenoidisynteesiin vaikuttavat entsyymit oli poistettu geneettisin menetelmin.
URI: URN:ISBN:978-952-10-3246-2
http://hdl.handle.net/10138/23164
Date: 2007-05-19
Copyright information: This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.
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