Biochimica et Biophysica Acta 1401Ž. 1998 242±264 View metadata, citation and similar papers at core.ac.uk brought to you by CORE Review provided by Elsevier - Publisher Connector Evolution and regulatory role of the hexokinases Marõa Luz Cardenas a, Athel Cornish-Bowden a,), Tito Ureta b a Institut Federatif Biologie Structurale et Microbiologie, Laboratoire de Chimie Bacterienne,  Centre National de la Recherche Scientifique, 31 chemin Joseph-Aiguier, 13402 Marseille Cedex 20, France b Departamento de Biologõa, Facultad de Ciencias, UniÕersidad de Chile, Casilla 653, Santiago, Chile Received 19 September 1997; revised 24 November 1997; accepted 27 November 1997 Keywords: Evolution; Hexokinase; Glucokinase Contents 1. Introduction ................................................... 243 2. General characteristics of glucose-phosphorylating enzymes ...................... 243 2.1. Isoenzymes ................................................ 243 2.2 Sugar specificity ............................................. 243 2.3 Specificity of the putative ancestral hexokinase........................... 245 2.4 Hexokinases and transporters ..................................... 246 2.5 Nucleotide triphosphate specificity .................................. 248 2.6 Molecular mass.............................................. 248 2.7 Hexokinase DŽ. or glucokinase? .................................... 249 3. Functional organization of the hexokinases ................................ 250 3.1 Inhibition by glucose 6-phosphate................................... 250 3.2 Two active sites on hexokinase B: kinetic consequences ..................... 252 3.3 Inhibition of hexokinase C by excess glucose ............................ 253 3.4 Functional adaptation of the rat isoenzymes ............................. 254 4. Similarities in primary structure of hexokinases ............................. 255 4.1 Rat isoenzymes .............................................. 255 4.2 Low molecular mass hexokinases ................................... 257 4.3 Phylogenetic relationships between hexokinases .......................... 258 4.4 Structural similarities with other proteins .............................. 259 5. Acknowledgements .............................................. 261 References ..................................................... 261 ) Corresponding author. Fax: q33-491-71-89-14; E-mail: [email protected] 0167-4889r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S0167-4889Ž. 97 00150-X M.L. Cardenas et al.rBiochimica et Biophysica Acta 1401() 1998 242±264 243 1. Introduction isoenzymes were first reported in rodent liverwx 14±18 , but appear to be characteristic of all animals, includ- The hexokinase-catalysed phosphorylation of glu- ing the humanwx 19,20 . Isoenzymes have also been cose by ATP occurs in all eukaryotic cells as the first found in green plantswx 21 and in several, but not all, step in the utilization of glucose, and the reaction is invertebrate species so far examinedwx 7 . Vertebrate also widespread in prokaryotic cells; the subsequent tissues contain up to four isoenzymes, designated as steps vary, as the glucose 6-phosphate formed in the hexokinases A, B, C and Dwx 18 on the basis of their first step may have different metabolic fates in differ- electrophoretic mobility; the alternative names hexok- ent types of cell and in different physiological condi- inases types I, II, III and IV, respectively, given by tions. Much information on hexokinases from differ- Katzen et al.wx 22 , are in widespread use; hexokinase ent species has accumulated since the pioneering DŽ. or IV is often called `glucokinase', but, as we work of Meyerhofwx 1 on yeast hexokinase, and there shall discuss in Section 2.7, this name is unfortunate are reviews on various aspects, including kinetics, because the four isoenzymes do not differ in their structure, and geneticswx 2±9 . specificity for glucose. Glucose is the preferred substrate of the hexoki- Comparisons between the isoenzymes from vari- nases, but they can also phosphorylate other hexoses ous sources has led several groups to suggest that to varying degrees, as recognized by the recom- evolution of the vertebrate hexokinases involved du- mended name of hexokinaseŽ ATP:D-hexose 6-phos- plication and fusion of an ancestral hexokinase of 50 photransferase, EC 2.7.1.1. Only a few species, es- kDa that resembled the present-day yeast hexokinases pecially bacteria, are known to contain true glucoki- and mammalian hexokinase D in sizewx 4,7,9,23±26 . nasesŽ ATP:D-glucose 6-phosphotransferase, EC We shall discuss this question in Section 4. 2.7.1.2. , i.e., enzymes specific for glucosewx 7 . Hexokinases from different species differ in 2.2. Sugar specificity molecular mass and tissue distribution, and the en- zyme often exists as a mixture of isoenzymes that It is widely believed that specificity has increased differ in kinetic characteristics and molecular mass. during evolution, i.e., that the more specific enzymes In this review, we first give a broad picture of the evolved from less specific ancestral proteinswx 27±29 , general characteristics of the hexokinases in different but one should not expect from this that the simpler phyla; we discuss whether a single kinetic model can modern organisms will have less specific enzymes be used to rationalize the kinetic and regulatory than the more complex organisms, because all mod- properties of the hexokinases; finally, we examine ern organisms have evolved to a high degree of similarities in primary structures and on the basis of efficiency in occupying particular ecological niches. sequence alignments propose a phylogenetic tree and As we will discuss in Section 3.4, at least three of the model of molecular evolution to explain it. four hexokinase isoenzymes in the rat have kinetic properties that correlate well with the functions of the organs in which they predominate, and there is no 2. General characteristics of glucose-phosphorylat- reason to doubt that a similar degree of adaptation ing enzymes exists in other organisms. Explanation for any differ- ences in enzyme specificity between different types 2.1. Isoenzymes of organisms should therefore be sought in differ- ences in their present-day requirements and not in Multiple hexokinases were first demonstrated in any supposed closeness to their ancestors. yeastwx 10 , which has three isoenzymes, hexokinases Examination of the glucose phosphorylating en- wx PIIIŽ. or A and P Ž. or B , and glucokinase 2,11±13 . zymes across the phylaŽ. Table 1 shows substantial The existence of distinct isoenzymes was shown not variation in hexose specificity, with the more specific only in diploid strains, in which hexokinases PI and enzymes found generally in the simpler organisms; PII could have been dismissed as allelic variants, but animals lack enzymes with high specificity for phos- also in haploid strainswx 12,13 . In animals, hexokinase phorylation of glucose, mannose or fructose at posi- 244 M.L. Cardenas et al.rBiochimica et Biophysica Acta 1401() 1998 242±264 Table 1 Specificity of hexokinases in different organisms Taxon High specificity Intermediate specificity Low specificity Archaeaa Pyrococcus furiosus wx30 Bacteriab Streptococcus mutans wx31 Leuconostoc meserentoides wx32 Escherichia coli wx33 E. coli wx34 Streptomyces Õiolaceruber wx35 Bacillus stearothermophilus wx36 E. coli wx37 Zymomonas mobilis wx38 Aerobacter aerogenes wx39 Rhodospirillum rubrum wx40 Pseudomonas saccharophila wx41 BreÕibacterium fuscum wx42 Lower eukaryotes Euglena gracilis wx43 Saccharomyces cereÕisiae w11,44 xSac. cereÕisiae wx45 Dictyostelium discoideum wx46 Torulopsis holmii wx47 Neurospora crassa wx48 Candida sp.wx 49 Saprolegnia litoralis wx40 Entamoeba histolytica wx50 Sap. litoralis wx40 Trypanosoma equiperdum wx51 Green plants Peaswx 52 Wheat w 53,54 x Animals Lobsterwx 55 Vertebrates w 4,56 x aThe Archaea were formerly called Archaebacteria. The more recent name reflects recognition that these organisms constitute a domain of life distinct from the bacteriawx 57 . bThe Bacteria were known as Eubacteria during the period when the Archaea were regarded as members of the same kingdomwx 57 . tion 6, whereas bacteria, apart from E. coli wx33 , have 2-deoxyglucose; however, unlike them and all other no unspecific hexokinases, and all of those that have known hexokinases it uses ADP as phosphate donor been described are either highly specific or at least Ž.and hence has AMP as a product and has no more specific than the enzymes of higher animals. detectable activity with ATP or other potential donors Prokaryotes and lower eukaryotes typically contain such as GDP or pyrophosphate. The authors suggest a series of specific hexokinases that each act on one that the specificity for ADP is related to the ability of hexose only, normally glucose, mannose or fructose; the organism to activate sugars after a period of in Pse. saccharophila, for example, glucokinase, starvation, i.e., in conditions of very low energy fructokinase and mannokinase exist as separate en- charge. By contrast, the thermoacidophile Sulfolobus zymeswx 41 , and various other organisms have spe- solfataricus appears to use ATP, but the enzyme cific glucokinases, such as E. coli wx34 , Z. mobilis responsible was studied only in cell homogenates, wx38,58 , B. stearothermophilus w36,59,60 x , Myxococ- and although these homogenates could also phospho- cus coralloides wx61 , S. mutans wx31 , A. aerogenes rylate fructose there