Magnús Már Kristjánsson

Professor at School of Engineering and Natural Sciences, Faculty of Physical Sciences, University of Iceland.


E-mail: mmk (at)

Phone: +354-525-4800/4819

Department of Biochemistry, Science Institute, Dunhagi 3, 107 Reykjavík

B.Sc. in Food Science, University of Iceland,1980.

M.Sc. in Food Chemistry, University of California, Davis, 1983.

Ph.D. in Food chemistry (major), Biochemistry and Nutrition (minors). Cornell University, New York, 1988.

Senior Research Scientist at Marine Biotechnology Center, Technical University of Denmark, Lyngby (1988-91)

Research Scientist at Department of Chemistry, Science Institute, University of Iceland. 1991-98.

Associate Professor of Food chemistry, Department of Food Science, Faculty of Physical Science, 1999-2008.

Associate Professor of Biochemistry, Department Chemistry, Faculty of Physical Sciences, School of Engineering and Natural Sciences, University of Iceland, 2008-2009. Full Professor since 2009.



The main focus of research of our group is on structure function relationships of proteins as they relate to temperature adaptation. We are especially interested in determining the  structural basis for the striking differences in both stability and catalytic properties of enzymes which have adapted to function at the extremes of temperature in the Biosphere.

At present the focus is on subtilisin-like serine proteinases (subtilases) from a psychrophilic Vibrio-species (VPR) and aqualysin I (AQUI), from the extreme thermophile Thermus aquaticus. We have determined several of the structural and functional properties of these enzymes, as well as related homologs. Comparative studies of these closely related subtilases have established their remarkably different properties with respect to catalytic activity and stability, reflecting their respective temperatures of adaptation. The crystal structures of VPR and AQUI, as well as of related homologs, are the subject of our structural comparisons on which we base hypotheses on the structural basis of  their temperature adaptation.

We focus on different aspects of temperature adaptation:

1) We use site directed mutagenesis to test hypotheses regarding structural basis of temperature adaptation of these subtilases. Several mutants of the cold adapted VPR and the heat adapted AQUI have been produced and characterized with respect to enzymatic properties and stability. Structural aspect which we have studied, or are studying, in this respect include the effects salt bridges, prolines in loops, hydrophobic packing and surface exposure, Ser-to Ala mutations, as well as differences in calcium binding sites.

2) We study molecular flexibility in the subtilases. Adjustment of molecular flexility is considered to play a key role in the temperature adaptation of proteins. Thus the higher catalytic activity of cold adapted enzymes when compared to thermophilic homologs, is suggested to reflect their higher molecular flexibility, whereas the high thermal stability of thermophilic proteins, reflect their rigid structures. In our research model we use site directed spin labeling (SDSL) and electroparamagnetic measurement (EPR), and fluoerescence spectroscopy to monitor dynamic movements in the structures of wild type and mutants of VPR and AQUI. Furthermore, in collaboration with Dr. Eleana Papaleo, at the University of Copenhagen, we study flexibilities of the VPR, AQUI and their mutants by molecular dynamics (MD) simulations.

3) We use the knowledge base obtained for the multitude of mutants of both VPR and AQUI to rationally design new properties in variants of the enzymes.

Ongoing project: The role of molecular flexibility in temperature adaptation of subtilises


Kristinn Ragnar Óskarsson, PhD student (biochemistry)

Arnór Freyr Sævarsson, MSc student (biochemistry)

Publications: PubMed

Personal Profile: GoogleScholar

Selected publications:

Óskarsson, K.R., Nygaard, M., Ellertsson, B.Ö., Thorbjarnardóttir, S., Papaleo, E. & Kristjánsson, M.M. (2016). A single mutation Gln142Lys doubles the catalytic activiity of VPR, a cold adapted subtilising-like serine proteinase. Biochim. Biophys. Acta 1864, 1436-1443.

Jónsdóttir LB, Ellertsson BO, Invernizzi G, Magnúsdóttir M, Thorbjarnardóttir SH, Papaleo E, Kristjánsson MM. The Role of Salt Bridges on the Temperature Adaptation of Aqualysin I, a Thermostable Subtilisin-like Proteinase. Biochim Biophys Acta. 2014 Aug 27;1844(12):2174-2181.

Sigtryggsdóttir, Á.S., Papaleo, E., Thorbjarnardóttir, S. H. & Kristjánsson, M.M. (2014). Flexibility of cold- and heat-adapted subtilisin-like serine proteinases evaluated with fluorescence quenching and molecular dynamics. Biochim. Biophys. Acta 1844, 705-712.

Kristjánsson, M. M. (2013) Cold adapted subtilases. In: Handbook of Proteolytic Enzymes (3rd ed.), (N.D. Rawling & G.G. Salvesen, Eds.), Chapter 695, pp. 3161-3166. AcademicPress/Elsevier, Oxford

Kristjánsson, M. M. (2012). Thermostable subtilases (subtilisin-like serine proteinases) In: Thermostable Proteins. Structural Stability and Design. (S. Sen & L. Nilsson, eds),pp.67-104. Taylor & Francis/CRC Press. Boca Raton, Florida.

Arnórsdóttir, J., Magnúsdóttir, M., Friðjónsson. Ó. H. & Kristjánsson, M. M. (2011) The effect of deleting a putative salt bridge on the properties of the thermostable subtilisin-like proteinase, aqualysin I. Protein Peptide lett. 18. 545-551.

Sigurdardóttir, A. G., Arnórsdóttir, J., Thorbjarnardóttir, S. H., Eggertsson, G., Suhre, K. & Kristjánsson, M. M. (2009) Characteristics of mutants designed to incorporate a new ion pair into the structure of a cold adapted subtilisin-like serine proteinase, Biochim. Biophys. Acta 1794, 512-518.

Arnórsdóttir, J, Sigtryggsdóttir, Á. R., Thorbjarnardóttir, S. H. &  Kristjánsson, M. M. (2009) Effect of proline substitutions on stability and kinetic properties of a cold adapted subtilase  
J. Biochem. 145, 325-329.

Kristjánsson, M. M. & Magnússon,  Ó. Þ. (2007) Rannsóknir á stöðugleika subtilísín-líks serín próteinasa (VPR) úr kuldakærri Vibrio sjávarbakteríu. Samanburður við samstofna ensímin, próteinasa K og aqualysin I. RH-report (RH-11-2007)

Arnórsdóttir, J., Helgadóttir, S., Thorbjarnardóttir, S. H., Eggertsson, G. and Kristjánsson, M. M. (2007) Effect of selected Ser/Ala and Xaa/Pro mutations on the stability and catalytic properties of a cold adapted subtilisin-like serine proteinase. Biochim. Biophys. Acta. 1774, 749-755.

Kristjánsson, M. M. (2006) Lífið í kulda. In: Vísindin heilla, (Book published in honour of prof. emeritus Sigmundur Guðbjarnarson), Háskólaútgáfan 2006. (in Icelandic)

Kristjánsson, M. M. (2006) Sameindalegar forsendur kuldaaðlögunar próteina. Nokkrar staðreyndir og vangaveltur. Tímarit um raunvísindi og stærðfræði (4. Árg) 1. Hefti.  (in Icelandic)

Arnórsdóttir, J., Kristjánsson, M. M. & Ficner, R. (2005) Crystal structure of a subtilisin-like serine protienase from a psychrotrophic Vibrio species reveals structural aspects of cold adaptation. FEBS Journal 272, 832-845.

Arnórsdóttir, J., Smáradóttir, R. B., Magnússon, Ó. Th., Thorbjarnardóttir, S. H., Eggertsson, G. and Kristjánsson, M. M. (2002)  Characterization of a cloned subtilisin-like serine proteinase from a psychrotrophic Vibrio-species. Eur. J. Biochem. 269, 5536-5546.

Kristjánsson, M. M. & Ásgeirsson, B. (2002) Properties of extremophilic enzymes and their importance for food science and technology. In Handbook of Food Enzymology. (Whitaker, J, Voragen, F., Wong, D. & Beldman, G, eds.) Chapter 8. pp.77-100. Marcel Decker, Inc. 

Kristjánsson, M.M. & Magnússon, Ó. Th. (2001) Effect of lyotropic salts on the stability of a subtilisin-like proteinase from a psychrotrophic Vibrio-species, proteinase K and aqualysin I. Protein Peptide Lett. 8, 249-255.

Kristjánsson, M. M. (2001) Activity measurements of proteases using synthetic substrates. In Current Protocols in in Food Analytical Chemistry (Wrolstad et al., eds.) John Wiley & Sons, Inc., New York.

Kristjánsson, M.M., Magnússon, Ó.Þ, Magnússon, H.M., Alfreðsson, G.Á.,. & Matsuzawa, H. (1999) Properties of a subtilisin-like proteinase from a psychrotrophic Vibrio-species. Comparison to proteinase K and aqualysin I. Eur. J. Biochem. 260, 752-760.

Kristjánsson, M.M., Ásgeirsson, B. & Bjarnason,J.B. (1997) Serine proteinases from cold-adapted organisms. In "Food Proteins and Lipids" (S. Damodaran, ed.) pp. 27-46. Plenum Press, New York.

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