Resultados

The ahgnments of the L, M, D1 and D2 sequences and structures (figures 3.1, 3.2 and 3.3, see also table 3.1 for a key to the codes) identifies the conserved residues some of which are likely to be those with key

structural and functional roles. Obvious examples of this are the histidine residues th a t co-ordinate the non-haem iron (His215 and 272 in D1 and His215 and 269 in D2) and the special-pair chlorophyll molecules (His 198 in D1 and D2).

The serine residue th at is believed to bind to Qg and upon certain mutations confers some herbicide resistance (Trebst, 1987) is conserved between D1 (Ser264) and L. The glutamate residue in L (Glul04) th a t hydrogen bonds to the bacteriopheophytin is also found in the conserved position (Glul30) in the higher plant D1 sequences.

There are particular residues th a t are involved in assisting electron transport in the purple non-sulphur bacteria reaction centres (see sections under 1.5.4). Some of these key residues may be conserved in the higher

plant alignment most notably Trp254 in D2. This residue, which in Rps.

viridis (Trp250) is in contact with both the bacteriopheophytin and Q^, is

conserved across the alignment between D2 and M but is a phenylalanine in the D1 and L equivalent positions.

Those residues th a t have a specific fimction in PS II, such as those binding the cofactors involved in water oxidation, are hkely to be conserved in PS II sequences only. The two redox active tyrosine residues a t position 161 in both D1 and D2 are totally conserved in the oxygenic organisms. This observation is expected given the key role in electron transport of these two amino acids. The equivalent residues in the bacterial reaction centre structures are not conserved and this difference highlights the variance in the methods used by the two systems for re-reducing the primary donor (see section 1 .8 .6 ).

There are a series of residues th at are likely to be charged th a t are also conserved, particularly in D l. These conserved residues include Aspl70, His332, Glu333 and Ala344 in D l which have all been implicated in binding the OEC (see section 1.8.5), as well as His337, Asp342, all of which have no equivalents in D2.

T ab le 3.1 Codes used in figures 3.1, 3.2 and 3.3, cross-referenced with those found in the OWL database (Bleasby and Wootton, 1990) and the organism and gene product names.

Code in Figures

Code in OWL database

Organism and Gene product

alfdl PSBA$MEDSA Alfalfa psbA

b a rd l PSBA$HORVU Barley psbA

bard2 PSBD$HORVU Barley psbl>

caldl PSBA$FREDI Calothrix psbA

chmodl PSBA$CHLMO Chlamydomonas moewusii psbA

chredl PSBA$CHLRE Chlamydomonas reinhardtii psbA

chred2 PSBD$CHLRE Chlamydomonas reinhardtii p s6 D

cfixl RCEL$CHLAU Chloroflexus aurantiacus psbA

cflxm RCEM$CHLAU Chloroflexus aurantiacus psbT>

cypadl PSBA$CYAPA Cyanophora paradoxa psbA

eugdl PSBA$EUGGR Euglena gracilis psbA

livdl FMLV32 Liverwort psbA

livd2 F2LVD2 Liverwort psbD

peadl PSBA$PEA Pea psbA

pead2 F2PMD2 Pea psbD

prcldl PSBA$PROHO Prochlorothrix hollandica psbA

rcapm RCEM$RHOCA Rhodobacter capsulatus pufM.

ricedl FMRZ32 Rice psbA

riced2 F2RZD2 Rice psbD

rrubl RCEL$RHORU Rhodospirillum rubrum pufL

rrubm RCEM$RHORU Rhodospirillum rubrum pufM.

ryedl PSBA$SECCE Rye psbA

ryed2 PSBD$SECCE Rye p s6 D

soydl FMSY32 Soybean psbA

spind2 F2SPD2 Spinach psbJ)

si WNRFLS Rhodobacter sphaeroides pufL

sm WNFRMS Rhodobacter sphaeroides pufL

sy7adl PSB2$SYNP7 Synechococcus PCC 7942 psbA II syn7dl PSB1$SYNP7 Synechococcus PCC 7942 psbA II syn7d2 PSBD$SYNP7 Synechococcus PCC 7942 p s6 D

syndl PSBA$SYNY4 Synechocystis PCC 6714 psbA

tobdl FMSP32 Tobacco psbA

tobd2 F2NTD2 Tobacco p s6 D

vl RCEL$RHOVI Rhodopseudomonas viridis pufL

F ig u re 3.1 Sequence alignment of the D l and D2 proteins from oxygenic

organisms; the codes are described in table 3.1. The amino acid code is the standard one letter code.

O rder o f' sequence a lig n m e n t

b ardl- Barley ryedl- Rye ricedl- Rice

peadl- Garden pea soydl- Soybean tobdl- Tobacco alfdl- Alfalfa livdl- Liverwort vicfadl- French bean

chmodl- Chlamydomonas moewusii

chredl- Chlamydomonas reinhardtii

cypadl- Cyanophora paradoxa

syn7dl- Synechococcus sp. (STRAIN PCC 7942) (Dl syTadl- Synechococcus sp. (STRAIN PCC 7942) (Dl syndl- Synechocystis sp.

caldl- Calothrix sp. (STRAIN PCC 7601) prcldl- Prochlorothrix hollandica

eugdl- Euglena gracilis

syn6 dl- Synechocystis sp. (STRAIN PCC 6803)

pead2 - Garden pea

tobd2 - Tobacco spind2 - Spinach riced2 - Rice ryed2 - Rye bard2 - Barley livd2 - Liverwort

chred2 - Chlamydomonas reinhardtii

- M T A I L E R - - R E S T S L W G R F C N W I T S T E N R L Y I G W F G V L M I P T L L T A T S V F I I A F I A A P P V D I D G I R E P V - M T A I L E R - - R E S T S L W G R F C N W I T S T E N R L Y I G W F G V L M I P T L L T A T S V F I l A F I A A P P V D I D G I R E P V - M T A I L E R - - R E S T S L W G R F C N W I T S T E N R L Y I G W F G V L M I P T L L T A T S V F I I A F I A A P P V D I D G I R E P V - M T A I L E R - - R D S E N L W G R F C N W I T S T E N R L Y I G W F G V L M I P T L L T A T S V F I l A F I A A P P V D I D G I R E P V - M T A I L E R - - R E S E S L W G R F C N W I T S T E N R L Y I G W F G V L M I P T L L T A T S V F I l A F I A A P P V D I D G I R E P V - M T A I L E R - - R E S E S L W G R F C N W I T S T E N R L Y I G W F G V L M I P T L L T A T S V F I I A F I A A P P V D I D G I R E P V - M T A I L E R - - R D S E T L W G R F C N W I T S T E R N L Y I G W F G V L M I P T L L T A T S V F I I A F I A A P P V D I D G I R E P V - M T A T L E R — R E S A S I W G R F C D W V T S T E N R L Y I G W F G V L M I P T L L T A T S V F I l A F I A A P P V D I D G I R E P V - M T A I L E R — R D S H N L W G R F C N W I T T T E N R L Y I G W F G V L M I P T L L T A T S V F I I A F I A A P P V D I D G I R E P V - M T A I L E R — R E S T S L W A R F C E W I T S T E N R I Y I G W F G V I M I P T L L T A T S V F I l A F I A A P P V D I D G I R E P V - M T A I L E R - - R E N S S L W A R F C E W I T S T E N R L Y I G W F G V I M I P C L L T A T S V F I l A F I A A P P V D I D G I R E P V - M T A T L E R - - N A S V S L W E Q F C G F I T S T E N R L Y I G W F G V L M F P L L L T A T T L F I I A F V A A P P V D I D G I R E P V - M T T A L Q R - - R E S A S L W Q Q F C E W V T S T D N R L Y V G W F G V L M I P T L L T A T I C F I V A F I A A P P V D I D G I R E P V - M T S I L R E — Q R R D N V W D R F C E W V T S T D N R I Y V G W F G V L M I P T L L T A T I C F I V A F I A A P P V D I D G I R E P V - M T T T L Q Q - - R E S A S L W E Q F C Q W V T S T N N R I Y V G W F G T L M I P T L L T A T T C F I I A F I A A P P V D I D G I R E P V - M T T T L Q Q — R S R A S V W D R F C E W I T S T E N R I Y I G W F G V L M I P T L L A A T A C F V I A F I A A P P V D I D G I R E P V - M T T A L R Q - - R E S A N A W E Q F C Q W I A S T E N R L Y V G W F G V I M I P T L L T A T I C F I I A F I A A P P V D I E X 3 I R E P V M I S P V L K K — Y A R P S L W Y R F C A W V A S K K N R L Y V G W F G V L M I P T L L T A A T V F I l A F I A A P P V D I D G I R E P V - M T T T Q L G — L Q E Q S L W S R F C C W I T S T S N R L Y I G W F G V L M I P T L L T A T T C F I I A F I A A P P V D I D G I R E P I - M T I A L G K F T K D Q N D L F D I M D D W L - R R D R F V F V G W S G L L L F P C A Y F A V G G W F T G T T F V T S W Y T H G L - M T I A L G K F T K D E N D L F D I M D D W L - R R D R F V F V G W S G L L L F P C A Y F A V G G W F T G T T F V T S W Y T H G L - M T I A V G K F T K D E K D L F D S M D D W L - R R D R F V F V G W S G L L L F P C A Y F A L G G W F T G T T F V T S W Y T H G L - M T I A L G R V T K E E N D L F D I M D D W L - R R D R F V F V G W S G L L L F P C A Y F A L G G W F T G T T F V T S W Y T H G L - M T I A L G R I P K E E N D L F D T M D D W L - R R D R F V F V G W S G L L L F P C A Y F A L G G W F T G T T F V T S W Y T H G L - M T I A L G R V P K E E N D L F D T M D D W L - R R D R F V F V G W S G L L L F P C A Y F A L G G W F T G T T F V T S W Y T H G L - M T I A I G K S S K E P K G L F D S M D D W L - R R D R F V F V G W S G L L L F P C A Y F A L G G W F T G T T F V T S W Y T H G L - M T I A I G T Y - Q E K R T W F D D A D D W L - R Q D R F V F V G W S G L L L F P C A Y F A L G G W L T G T T F V T S W Y T H G L - M T I A V G R A P - A E R G W F D V L D D W L - K R D R F V F V G W S G L L L F P C A Y L A L G G W L T G T S F V T S W Y T H G I S G S L L Y G N N I I S G A I I P T S A A I G L H F Y P I W - - E A - A S V D E W L Y N G G P Y E L I V L H F L L G V A C Y M G R E W E L S S G S L L Y G N N I I S G A I I P T S A A I G L H F Y P I W - - E A - A S V D E W L Y N G G P Y E L I V L H F L L G V A C Y M G R E W E L S S G S L L Y G N N I I S G A I I P T S A A I G L H F Y P I W - - E A - A S V D E W L Y N G G P Y E L I V L H F L L G V A C Y M G R E W E L S S G S L L Y G N N I I S G A I I P T S A A I G L H F Y P I W - - E A - A S V D E W L Y N G G P Y E L I V L H F L L G V A C Y M G R E W E L S S G S L L Y G N N I I S G A I I P T S A A I G L H F Y P I W - - E A - A S V D E W L Y N G G P Y E L I V L H F L L G V A C Y M G R E W E L S S G S L L Y G N N I I S G A I I P T S A A I G L H F Y P I W - - E A - A S V H E W L Y N G G P Y E L I V L H F L L G V A C Y M G R E W E L S S G S L L Y G N N I I C G A I I P T S A A I G L H F Y P I W - - E A - A S V D E W L Y N G G P Y E L I V L H F L L G V A C Y M G R E W E L S