Evolutionary aspects of cytochromec oxidase

The presence of additional subunits in cytochrome oxidase distinguish the multicellular eukaryotic enzyme from that of a simple unicellular bacterial enzyme. The number of these additional subunits increases with increasing evolutionary stage of the organism. Subunits I–III of the eukaryotic enzyme are related to the three bacterial subunits, and they are encoded on mito-chondrial DNA. The additional subunits are nuclear encoded. Experimental evidences are presented here to indicate that the lower enzymatic activity of the mammalian enzyme is due to the presence of nuclear-coded subunits. Dissociation of some of the nuclear-coded subunits (e.g., VIa) by laurylmaltoside and anions increased the activity of the rat liver enzyme to a value similar to that of the bacterial enzyme. Further, it is shown that the intraliposomal nucleotides influence the kinetics of ferrocytochromec oxidation by the reconstituted enzyme from bovine heart but not fromP. denitrificans. The regulatory function attributed to the nuclear-coded subunits of mammalian cytochromec oxidase is also demonstrated by the tissue-specific response of the reconstituted enzyme from bovine heart but not from bovine liver to intraliposomal ADP. These enzymes from bovine heart and liver differ in the amino acid sequences of subunits VIa, VIIa, and VIII. The results presented here are taken to indicate a regulation of cytochromec oxidase activity by nuclear-coded subunits which act like receptors for allosteric effectors and influence the catalytic activity of the core enzyme via conformational changes.     

Evolutionary aspects of hair polymorphism

Polymorphism of hair was considered in terms of their origin in mammalian evolution. Vibrissae significantly differ from hairs by the structure. Apparently, they originated from mechanoreceptors of Cotylosauria and developed only in the Theriodontia-Cynodontia-Panthotheria-Theria lineage (Metatheria, Eutheria). No vibrissa developed in the lineage of Theriodontia-Cynodontia-Prototheria (Multituberculata, Triconodonta, Monotremata), where mechanoreceptors or glandular structures of amphibian ancestors transformed into electro-and mechanoreceptors. Hairs originated in these lineages in parallel from keratin epidermis in correlation with the establishment of homeothermy but independently of vibrissae. Wide and active adaptive radiation provided for a strong differentiation of hairs largely similar in different taxa. Spines originated by heterochrony of hair generations.     

Evolutionary aspects of whole-genome biology

A decade of access to whole-genome sequences has been increasingly revealing about the informational network relating all living organisms. Although at one point there was concern that extensive horizontal gene transfer might hopelessly muddle phylogenies, it has not proved a severe hindrance. The melding of sequence and structural information is being used to great advantage, and the prospect exists that some of the earliest aspects of life on Earth can be reconstructed, including the invention of biosynthetic and metabolic pathways. Still, some fundamental phylogenetic problems remain, including determining the root--if there is one--of the historical relationship between Archaea, Bacteria and Eukarya.     

Evolutionary aspects of bat echolocation

This review is yet another attempt to explain how echolocation in bats or bat-like mammals came into existence. Attention is focused on neuronal specializations in the ascending auditory pathway of echolocating bats. Three different mechanisms are considered that may create a specific auditory sensitivity to echos: (1). time-windows of enhanced echo-processing opened by a corollary discharge of neuronal vocalization commands; (2). differentiation and expansion of ensembles of combination-sensitive neurons in the midbrain; and (3). corticofugal top-down modulations. The second part of the review interprets three different types of echolocation as adaptations to ecological niches, and presents the sophisticated cochlear specializations in constant-frequency/frequency-modulated bats as a case study of finely tuned differentiation. It is briefly discussed how a resonant mechanism in the inner ear of constant-frequency/frequency-modulated bats may have evolved in common mammalian cochlea.     

Evolutionary aspects of primate locomotion

Both neontological and phylogenetic studies are necessary to interpret primate locomotion. Reference to palaeoprimatology and palaeocology, for instance, will lead to a fuller understanding of the roots of such gaits as the vertical clinging and leaping of Tarsius, Indri and Propithecus. Evolutionary trends in posture and locomotion are discussed. The postural trend has been towards maintenance of trunk verticality and the locomotor trend towards an increasing dependence on the forelimbs among arboreal primates. Three stages are recognized in the phylogenetic course of arboreal locomotor adaptation: Stage A. Vertical clinging and leaping; Stage B. Quadrupedalism; Stage C. Brachiation. The role of prehensility of the hand in the evolution of locomotor types is discussed in relation to forest morphology and, in particular, to stratification. Finally a scheme of evolution, set in the framework of ecology, for Old World Monkey groups is presented.     

Evolutionary aspects of elemental hyperaccumulation

Hyperaccumulation is the uptake of one or more metal/metalloids to concentrations greater than 50–100× those of the surrounding vegetation or 100–10,000 mg/kg dry weight depending on the element. Hyperaccumulation has been documented in at least 515 taxa of angiosperms. By mapping the occurrence of hyperaccumulators onto the angiosperm phylogeny, we show hyperaccumulation has had multiple origins across the angiosperms. Even within a given order, family or genus, there are typically multiple origins of hyperaccumulation, either for the same or different elements. We address which selective pressures may have led to the evolution of hyperaccumulation and whether there is evidence for co-evolution with ecological partners. Considerable evidence supports the elemental-defense hypothesis, which states that hyperaccumulated elements protect the plants from herbivores and pathogens. There is also evidence that hyperaccumulation can result in drought stress protection, allelopathic effects or physiological benefits. In many instances, ecological partners of hyperaccumulators have evolved resistance to the hyperaccumulated element, indicating co-evolution. Studies on the molecular evolution of hyperaccumulation have pinpointed gene duplication as a common cause of increased metal transporter abundance. Hypertolerance to the hyperaccumulated element often relies upon chelating agents, such as organic acids (e.g., malate, citrate) or peptide/protein chelators that can facilitate transport and sequestration. We conclude the review with a summary and suggested future directions for hyperaccumulator research.     

Autophosphorylation of calmodulin kinase II: functional aspects

Autophosphorylation of purified calmodulin kinase II dramatically inhibited protein kinase activity and enhanced substrate selectivity. Inhibition was observed over a wide range of calmodulin concentrations but calmodulin binding was unaffected. Autophosphorylation of calmodulin kinase II may be a mechanism for limiting phosphorylation to physiological substrates and terminating some of calcium's actions in synaptic events.     

Evolutionary aspects of some neuropeptides.

The study of biologically active peptides is a study of structural homology and functional diversity. Some fundamental peptide structures used as chemical messengers by simple organisms were evidently maintained throughout evolution with little change. In higher organisms these structures may still be used for functions related to the original use as well as for very different purposes. Examples are given of the multifunctional roles of common peptides and of the mechanisms by means of which these functions are separated and regulated. The active core of ACTH appears to be used as a signal in regulation of reproduction throughout the range of eukaryotes and also appears in a baffling range of other important proteins. The ubiquitous nature of this peptide sequence suggests that it plays a universal role in recognition or activation of specific receptors. Peptides used in lower species as hormones or chemical defense substances play an important role in research as presagers of the discovery of corresponding mammalian peptides.     

Evolutionary aspects of the arthropod heart

Evolution has led to changes in the gross anatomy of the arthropod hearts. Changes are also seen in the ultrastructural organization of the cardiomyofiber. Thus the myofilament organization and the membrane systems (T-system and SR) vary within both Chelicerata, Crustacea and Uniramia. Yet, the variation is not haphazard, but constitutes a pattern which cannot be deduced from the gross anatomy. In the three taxa the evolutionary tendency seems to be towards a more strict sarcomeral organization of the myofilaments. This is due to parallelism. The organization of the membrane systems and the spatial relation of the interior couplings are not identical for all arthropods. However, no variations has so far been detected within one and the same order, despite differences in adaptation and size. These systems are conservative and it is suggested that they could be useful in studies of arthropod phylogeny.     

Evolutionary aspects of inorganic pyrophosphatase.

Based on the primary structure, soluble inorganic pyrophosphatases can be divided into two families which exhibit no sequence similarity to each other. Family I, comprising most of the known pyrophosphatase sequences, can be further divided into prokaryotic, plant and animal/fungal pyrophosphatases. Interestingly, plant pyrophosphatases bear a closer similarity to prokaryotic than to animal/fungal pyrophosphatases. Only 17 residues are conserved in all 37 pyrophosphatases of family I and remarkably, 15 of these residues are located at the active site. Subunit interface residues are conserved in animal/fungal but not in prokaryotic pyrophosphatases.     

Novel aspects of calmodulin target recognition and activation.

Several crystal and NMR structures of calmodulin (CaM) in complex with fragments derived from CaM-regulated proteins have been reported recently and reveal novel ways for CaM to interact with its targets. This review will discuss and compare features of the interaction between CaM and its target domains derived from the plasma membrane Ca2+-pump, the Ca2+-activated K+-channel, the Ca2+/CaM-dependent kinase kinase and the anthrax exotoxin. Unexpected aspects of CaM/target interaction observed in these complexes include: (a) binding of the Ca2+-pump domain to only the C-terminal part of CaM (b) dimer formation with fragments of the K+-channel (c) insertion of CaM between two domains of the anthrax exotoxin (d) binding of Ca2+ ions to only one EF-hand pair and (e) binding of CaM in an extended conformation to some of its targets. The mode of interaction between CaM and these targets differs from binding conformations previously observed between CaM and peptides derived from myosin light chain kinase (MLCK) and CaM-dependent kinase IIalpha (CaMKIIalpha). In the latter complexes, CaM engulfs the CaM-binding domain peptide with its two Ca2+-binding lobes and forms a compact, ellipsoid-like complex. In the early 1990s, a model for the activation of CaM-regulated proteins was developed based on this observation and postulated activation through the displacement of an autoinhibitory or regulatory domain from the target protein upon binding of CaM. The novel structures of CaM-target complexes discussed here demonstrate that this mechanism of activation may be less general than previously believed and seems to be not valid for the anthrax exotoxin, the CaM-regulated K+-channel and possibly also not for the Ca2+-pump.     

Evolutionary aspects of protein structure and folding

Four basic stages of evolution of protein structure are described based on recent work of the authors targeted specifically on reconstruction of the earliest events in the protein evolution. According to this reconstruction, the initial stage of short peptides of, probably, only few amino-acid residues had been followed by formation of closed loops of the size 25-30 residues, which corresponds to the polymer-statistically optimal ring closure size for mixed polypeptide chains. The next stage involved fusion of the respective small linear genes and formation of protein structures consisting of several closed loops of the nearly standard size, up to 4-6 loops (100-200 amino acid residues) in a typical protein fold. The last, modern stage began with combinatorial fusion of the presumably circular 300-600 bp DNA units and, accordingly, formation of multidomain proteins.     

Evolutionary aspects of protein structure and folding

The traditional reconstruction of molecular events of the past based on sequence conservation becomes very vague beyond one to two billion years ago. There are certain molecular features, however, such as polymer flexibility and loop closure, that are conserved merely because of their physical nature. This allows one to penetrate the earliest stages of protein evolution.