RESUMO
The solution structure of the leader sequence of the patellamide precursor peptide was analysed by using CD and determined with NOE-restrained molecular dynamics calculations. This leader sequence is highly conserved in the precursor peptides of some other cyanobactins harbouring heterocycles, and is assumed to play a role in targeting the precursor peptide to the post-translational machinery. The sequence was observed to form an alpha-helix spanning residues 13-28 with a hydrophobic surface on one side of the helix. This hydrophobic surface is proposed to be the site of the initial binding with modifying enzymes.
Assuntos
Proteínas de Bactérias/química , Precursores de Proteínas/química , Sequência de Aminoácidos , Dicroísmo Circular , Concentração de Íons de Hidrogênio , Espectroscopia de Ressonância Magnética , Simulação de Dinâmica Molecular , Dados de Sequência Molecular , Peptídeos/química , Prochloron/enzimologia , Sinais Direcionadores de Proteínas , Estrutura Secundária de Proteína , Alinhamento de Sequência , Homologia de Sequência de AminoácidosRESUMO
Photosynthetic organisms have a variety of accessory pigments, on which their classification has been based. Despite this variation, it is generally accepted that all chloroplasts are derived from a single cyanobacterial ancestor. How the pigment diversity has arisen is the key to revealing their evolutionary history. Prochlorophytes are prokaryotes which perform oxygenic photosynthesis using chlorophyll b, like land plants and green algae (Chlorophyta), and were proposed to be the ancestors of chlorophyte chloroplasts. However, three known prochlorophytes (Prochloron didemni, Prochlorothrix hollandica and Prochlorococcus marinus) have been shown to be not the specific ancestors of chloroplasts, but only diverged members of the cyanobacteria, which contain phycobilins but lack chlorophyll b. Consequently it has been proposed that the ability to synthesize chlorophyll b developed independently several times in prochlorophytes and in the ancestor of chlorophytes. Here we have isolated the chlorophyll b synthesis genes (chlorophyll a oxygenase) from two prochlorophytes and from major groups of chlorophytes. Phylogenetic analyses show that these genes share a common evolutionary origin. This indicates that the progenitors of oxygenic photosynthetic bacteria, including the ancestor of chloroplasts, had both chlorophyll b and phycobilins.
Assuntos
Clorofila/análise , Cloroplastos/química , Cianobactérias/química , Evolução Molecular , Oxigenases/genética , Ficocianina/análise , Pirróis/análise , Sequência de Aminoácidos , Animais , Arabidopsis/enzimologia , Arabidopsis/genética , Chlamydomonas reinhardtii/enzimologia , Chlamydomonas reinhardtii/genética , Cloroplastos/classificação , Cianobactérias/classificação , Cianobactérias/enzimologia , Cianobactérias/genética , Eucariotos/química , Eucariotos/enzimologia , Eucariotos/genética , Dados de Sequência Molecular , Ficobilinas , Filogenia , Prochloron/química , Prochloron/enzimologia , Prochloron/genética , Prochlorothrix/química , Prochlorothrix/enzimologia , Prochlorothrix/genética , Homologia de Sequência de Aminoácidos , TetrapirróisRESUMO
Prochloron is a genus of prokaryotic algae with photosynthetic pigments like those of chlorophytes. Prochlorophytes are almost invariably found associated as symbionts with marine protochordates (didemnid ascidians), and so far none has been successfully grown in sustained culture away from in host. Based on materials collected from nature, information of various sorts (biochemical, physiological, cytological and fine-structural) has been obtained, indicating many resemblances (and probably close phylogenetic affinities) between prochlorophytes and cyanophytes. Nevertheless they are distinguished by certain unique combinations of characters. Some of the data support the symbiogenesis theory for the origin of green-plant chloroplasts. Other possibilities are briefly discussed.
