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Toxic Plant Proteins

:	J. Michael Lord, Martin R. Hartley
:	J. Michael Lord, Martin R. Hartley
:	Toxic Plant Proteins
:	Springer-Verlag
:	9783642121760
:	1
:	CHF 132.50
:

:	Botanik
:	English

:	270
:	Wasserzeichen/DRM
:	PC/MAC/eReader/Tablet
:	PDF

Many plants produce enzymes collectively known as ribosome-inactivating proteins (RIPs). RIPs catalyze the removal of an adenine residue from a conserved loop in the large ribosomal RNA. The adenine residue removed by this depurination is crucial for the binding of elongation factors. Ribosomes modified in this way are no longer able to carry out protein synthesis. Most RIPs exist as single polypeptides (Type 1 RIPs) which are largely non-toxic to mammalian cells because they are unable to enter them and thus cannot reach their ribosomal substrate. In some instances, however, the RIP forms part of a heterodimer where its partner polypeptide is a lectin (Type 2 RIPs). These heterodimeric RIPs are able to bind to and enter mammalian cells. Their ability to reach and modify ribosomes in target cells means these proteins are some of the most potently cytotoxic poisons found in nature, and are widely assumed to play a protective role as part of the host plant's defenses. RIPs are able to further damage target cells by inducing apoptosis. In addition, certain plants produce lectins lacking an RIP component but which are also cytotoxic. This book focuses on the structure/function and some potential applications of these toxic plant proteins.

	Editors	6
	Preface	8
	Contents	10
	Evolution of Plant Ribosome-Inactivating Proteins	12
	1 Introduction	12
	2 General Overview of the Taxonomic Distribution of A and B Domains within the Viridiplantae	13
	3 Overview of the Taxonomic Distribution of A and B Domains within the Magnoliophyta (Flowering Plants)	15
	3.1 ``Classical´´ Type 2 RIPs (AB proteins)	15
	3.2 Other Proteins with Ricin- Domains	16
	4 Molecular Evolution of Type 2 RIPs	16
	4.1 General Observations Concerning the Taxonomic Distribution of Type 2 RIPs and the Occurrence of Multiple Paralogs	16
	4.2 Overall Phylogeny of Type 2 RIPs	17
	4.3 Special Evolutionary Events: Gene Amplification and Generation of Type A and Type B Proteins from Genuine Type 2 RIPs	19
	4.4 What is the Origin of Type 2 RIP Genes?	22
	4.4.1 Origin of the B-hain	22
	4.4.2 Origin of the A-hain	23
	5 Molecular Evolution of Type 1 RIPs	23
	5.1 Dicots and Monocots Other Than Poaceae	24
	5.2 Poaceae Type 1 RIPs	27
	5.2.1 O. sativa	27
	5.2.2 Andropogoneae: Z. mays and Sorghum bicolor	28
	5.2.3 Pooideae	29
	5.2.4 Relationships between the RIPs from Poaceae and Other Seed Plants	29
	6 What is the Relationship between Plant and Bacterial RIPs?	31
	7 Chimeric RIPs Other Than Type 2 RIPs	31
	7.1 JIP60 and Other Type AC Chimeric RIPs	31
	7.2 Chimeric RIP with a C-erminal D Domain	34
	8 Conclusions	34
	References	36
	RNA N-Glycosidase Activity of Ribosome-Inactivating Proteins	38
	1 Introduction	38
	2 Ricin as an RNA N-lycosidase	39
	2.1 28S rRNA as the Target of Modification by Ricin and Other RIPs	39
	2.2 RNA N-lycosidase Activity of Ricin A-hain	41
	2.3 Other RIPs	42
	2.4 Major Role of RNA in Protein Synthesis	42
	3 Ribosomal Mechanisms Involving the Sarcin-icin Domain	43
	3.1 Eukaryotic Translation Can Be Inhibited Strongly by Dysfunction of a Small Fraction of the Ribosome Population	43
	3.2 Difference in the Modes of Action between a-arcin and Ricin	43
	3.3 Substrate Specificity	44
	3.4 Structure of the SRL	44
	4 Ribosomal RNA Apurinic Site-pecific Lyase: Intrinsic Stability of the Ribosome	46
	References	48
	Enzymatic Activities of Ribosome-Inactivating Proteins	51
	1 Introduction	51
	2 Action of RIPs on Ribosomes and rRNA	52
	2.1 Site of Modification by RIPs	52
	2.2 Structural Requirements in Ribosomal RNA for RIP Action	53
	3 Polynucleotide:Adenosine Glycosidase Activity	56
	3.1 5 Cap-ndependent Activity	56
	3.2 5 Cap-ependent Activity	57
	4 DNA Lyase	59
	5 Bifunctional Enzymes with RIP Activity in Which the Non-IP Activity Acts on Non-ucleic Acid Substrates	59
	5.1 Lipase	59
	5.2 Chitinase	60
	5.3 Superoxide Dismutase	60
	6 Conclusions	61
	References	62
	Type I Ribosome-Inactivating Proteins from Saponaria officinalis	65
	1 Introduction	65
	2 Saporin Multigene Family and Saporin Isoforms	66
	3 Saporin Biochemical Features	68
	3.1 Saporin Structure	68
	3.2 Saporin Catalytic Activity	71
	3.3 Residues Important for the Catalytic Activity	72
	3.4 Interaction with the Ribosome	73
	3.5 Saporin Inhibitors	74
	4 Saporin Trafficking and Toxicity in Eukaryotic Cells	75
	4.1 Subcellular Distribution of Saporin Isoforms in Soapwort Tissues	75
	4.2 Saporin Biosynthesis and Role in Planta	76
	4.3 Intoxication Pathways in Mammalian Cells	77
	5 Heterologous Expression of Saporin and Saporin Fusion Toxins	80
	6 Conclusions and Perspectives	82
	References	82
	Type 1 Ribosome-Inactivating Proteins from the Ombú Tree (Phytolacca dioica L.)	89
	1 Introduction	89
	2 RIPs from P. dioica L.	90
	2.1 Isolation of RIPs from Seeds and Leaves of P. dioica	92
	2.2 Basic Characteristics of RIPs from Seeds and Leaves of P. dioica	92
	2.3 Differential Seasonal and Age Expression in Leaves	97
	2.4 Cellular Localization	98
	2.5 Glycosylation of P. dioica RIPs	98
	3 Enzymatic and Biological Characteristics	100
	3.1 Neta-lycosidase and APG Activities	100
	3.2 Toxicity to Mice	101
	3.3 Immunotoxin	101
	3.4 Cross-eactivity	102
	3.5 Activity on Double-tranded pBR322 DNA	102
	4 X-ay Crystal Structure of P. dioica RIPs	106
	4.1 Atomic Resolution Studies of PD-4: A Reference RIP Structure	106
	4.2 An Insight into the Active Site of PD-4: Tyr72 as a Substrate Carrier Through pi- Stacking Interactions with Aden	107
	4.3 PD-1 and PD-4 -Two Homologous Proteins with Distinct Functional Properties	110
	5 Concluding Remarks	111
	References	112