NMR Studies of Bacterial Albumin-Binding Modules

Abstract

Peptostreptococcus magnus and group C/G streptococci are Gram-positive cocci that are part of the normal flora and reside in more or less the same locations in the host.



Protein G of group C/G streptococci was originally described as binding IgGFc of several species and later shown to also bind human serum albumin and albumins from various animal species. From albumin-binding strains of P. magnus several albumin-binding proteins have been isolated, one of which is protein PAB (Peptostreptococcal Albumin Binding), containing a domain of 45 residues showing a high (59 %) degree of homology to the human serum albumin binding domains of protein G and which was therefore called the GA (protein G-related Albumin binding) module. It has been suggested that the GA module has been transferred from protein G into protein PAB recently and that it represents the first contemporary example of module shuffling (M. de Chateau and L. Björck, J. Biol. Chem., 269:12147-51, 1994).



The GA modules of protein PAB and protein G have been studied in this thesis. They are shown to be very stable and form three-helical bundles. It has been shown that they bind to the same site on human serum albumin, but that the GA module of protein PAB binds human serum albumin with higher affinity than the GA module of protein G does. It has also been shown that the GA module of protein G shows a broader albumin-binding specificity than the GA module of protein PAB. Group C/G streptococci infect virtually all mammalian species, whereas P. magnus has been isolated only from humans. During the relatively short time period when the protein G-GA of C/G streptococci has been part of protein PAB of P. magnus, its only function has therefore most likely been to bind human serum albumin. As a result the GA module of protein PAB binds non-primate albumins with much lower affinity than primate albumins, whereas for the GA module of protein G the difference in affinity between non-primate and primate is much less pronounced. Group C/G streptococci are known to infect most, if not all, mammalian species, and nearly all strains of these bacteria bind albumin. By comparison, P. magnus has only been seen to infect humans, and although most strains of P. magnus do not bind albumin, those that do have typically been isolated from patients with deep wound infections. The greater flexibility of the GA module of protein G seen from the Nitrogen-15 spin relaxation experiments is in line with its broad species specificity and, likewise for the less flexible GA module of protein PAB, which has narrow specificity and high affinity for human serum albumin. In view of the evolutionary relationship between the two GA modules our results suggest an evolution development during which the GA module of protein PAB has adapted to its environment, which contains only human serum albumin. This adaptation to the human host has led to a loss of molecular flexibility and a more narrow albumin-binding specificity.

Abstract (Swedish)

Popular Abstract in Swedish

Proteiner är uppbyggda av aminosyror som är hopkopplade med varandra och bildar långa kedjor som kan bestå av hundra- eller tusentals aminosyror. Det finns en mängd olika proteiner och de har många olika funktioner.



I studierna som beskrivs här, har proteiner som finns på ytan av vissa bakterier studerats. De långa proteinkedjorna i dessa bakteriella ytproteiner är ofta uppbyggda av kortare, sk modulära, segment bestående av ca 40-80 aminosyror. Moduler som binder till albumin, ett rikligt förekommande protein hos människa och andra djur som bakterierna infekterar, har studerats i avhandlingsarbetet. Genom att binda till albuminet anser man bl a att bakterien kan undgå att upptäckas av värddjurets immunsystem.



Två albumin-bindande moduler har studerats med avseende på, i huvudsak, struktur, dynamik och bindningsegenskaper. Ett intressant samband mellan dynamik och bindningsegenskaper kunde påvisas. Den ena albumin-bindande modulen som finns i bakterier som infekterar de flesta däggdjur, är mycket flexibel och binder bra till de flesta albuminer. Den andra studerade albumin-bindande modulen finns hos bakterier som bara infekterar människor. Den är betydligt mindre flexibel och binder betydligt svagare till icke-mänskligt albumin. Däremot binder den mycket bättre till mänskligt albumin, det albumin som bakterien och modulen haft anledning att specialisera sig på.

• author: Johansson, Maria U
• supervisor: [unknown] [unknown]
• opponent: Professor Clore, G. Marius, Laboratory of Chemical Physics, NIH, Bethesda, MD, USA
• organization: Biophysical Chemistry
• publishing date: 2002
• type: Thesis
• publication status: published
• subject: Physical Chemistry
• keywords: Fysikalisk kemi, Biotechnology, Bioteknik, Proteins, enzymology, Proteiner, enzymologi, Physical chemistry, three-helix bundle, protein structure, protein PAB, protein-protein interactions, protein G, protein dynamics, NMR, module shuffling, GA module, evolution, albumin-binding, bacterial surface proteins
• pages: 96 pages
• defense location: Lecture Hall D, The Center for Chemistry and Chemical Engineering, Getingevägen 60, Lund
• defense date: 2002-05-16 10:15:00
• external identifiers: other:ISRN: LUTKDH/TKFK--02/1011--SE
• ISBN: 91-628-5248-5
• language: English
• LU publication?: yes
• additional info: Article: The GA module, a mobile albumin-binding bacterial domain, adopts a three-helix-bundle structureJohansson, M. U., de Château, M., Björck, L., Forsén, S., Drakenberg, T. and Wikström, M.FEBS Letters 374, 257-61 (1995) Article: Solution structure of the albumin-binding GA module - a versatile bacterial protein domainJohansson, M. U., de Château, M., Wikström, M., Forsén, S., Drakenberg, T. and Björck, L.J. Mol. Biol., 266, 859-65 (1997) Article: Structure, specificity, and mode of interaction for bacterial albumin-binding modulesJohansson, M. U., Frick, I.-M., Nilsson, H., Kraulis, P. J., Hober, S., Jonasson, P., Linhult, M., Nygren, P.-Å., Uhlén, M., Björck, L., Drakenberg, T., Forsén, S. and Wikström, M.J. Biol. Chem., 277, 8114-20 (2002) Article: Differences in backbone dynamics of two homologous bacterial albumin-binding modules: Implications for binding specificity and bacterial adaptationJohansson, M. U., Nilsson, H., Evenäs, J., Forsén, S., Drakenberg, T., Björck, L. and Wikström, M.J. Mol. Biol., 316, 1083-99 (2002)
• id: a65a66e5-0928-4855-b68e-aee47d5307fc (old id 464627)
• date added to LUP: 2016-04-04 12:05:36
• date last changed: 2018-11-21 21:08:58