04 Tema 03 Proteinas 2011 Web

7/31/2019 04 Tema 03 Proteinas 2011 Web

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Protenas

Prof. Wilkesman

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Repasemos

la formacinde unaprotena


Amino Acid Sequences Have Direction

This illustration ofthe pentapeptideTyr-Gly-Gly-Phe-Leu (YGGFL)shows thesequence from theamino terminus tothe carboxylterminus


Proteins

are linear polymers built of monomer unitscalled amino acids.

contain a wide range of functional groups.

can interact with one another and withother biological macromolecules to form

complex assemblies. Some are quite rigid, whereas others

display limited flexibility


MW de protenas MW en g/mol

MW en Da

MW promedio de los aa= 110

N aa encontrados en prot.= 50-2000

MW prom de las protenas=?


Podemos clasificarlas? Fibrosas

Forma filamentosa

Funcin estructural en clulas y tejidos

Ej.: protenas de la piel, tejido conjuntivo, fibrasanimales

Globulares Forma de globo por plegado de la cadena

polipeptdica

Funciones: trabajo qumico de la clula

Ej.: Mioglobina, hemoglobina,


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Ej: Insulina

Amino Acid Sequence of Bovine Insulin.


Estructuras de organizacin enprotenas

Estructuras:

1 -> secuencia de aa 2 -> hlices , lminas

3 -> plegado de la estruct. 2

4 -> Empaquetado de estructuras 3


Hlices alfa

Structure of the Helix. (A) A ribbon depiction with the -carbon atoms and side chains (green) shown. (B) Aside view of a ball-and-stick version depicts the hydrogen bonds (dashed lines) between NH and CO groups. (C)An end view shows the coiled backbone as the inside of the helix and the side chains (green) projecting outward.(D) A space-filling view of part C shows the tightly packed interior core of the helix.


Lminas beta

Structureof a Strand. The side chains (green) are alternately above and belowthe plane of the strand


Lminasbeta An Antiparallel

Sheet.Adjacent strands run in oppositedirections. Hydrogenbonds between NH andCO groups connecteach amino acid to asingle amino acid on anadjacent strand,stabilizing the structure.

A Parallel Sheet.Adjacent strands runin the same direction.Hydrogen bondsconnect each aminoacid on one strand withtwo different aminoacids on the adjacentstrand.


Lminas beta mixtas

Structure of a Mixed Sheet


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Dihedral angles A measure of the rotation about a bond, usually between

-180 and +180. Sometimes called torsion angles

The structure of each amino acid in a polypeptide can be adjusted by rotation about two singlebonds. (A) Phi ( ) is the angle of rotation about the bond between the nitrogen and the -carbonatoms, whereas psi () is the angle of rotation about the bond between the -carbon and thecarbonyl carbon atoms. (B) A view down the bond between the nitrogen and the -carbonatoms, showing how is measured. (C) A view down the bond between the-carbon and thecarbonyl carbon atoms, showing how is measured.


ngulos derotacin

Rotation About Bonds in aPolypeptide. The structure of eachamino acid in a polypeptide can beadjusted by rotation about twosingle bonds. (A) Phi () is theangle of rotation about the bondbetween the nitrogen and the -carbon atoms, whereas psi (y) isthe angle of rotation about the bondbetween the -carbon and thecarbonyl carbon atoms. (B) A viewdown the bond between thenitrogen and the -carbon atoms,showing how is measured. (C) Aview down the bond between the -carbon and the carbonyl carbonatoms, showing how y ismeasured.


Convenio


Representaciones deRamachandran

Ilustracin que representa lasconformaciones permitidas. Pueden existirmuchas combinaciones de estructurassecundarias, pero slo algunas son

factibles. Las coordenadas son losngulos psi () y phi ()


A Ramachandran Diagram Showing the Values of and psi. Not all and psivalues are possible without collisions between atoms. The most favorable regions areshown in dark green; borderline regions are shown in light green. The structure onthe right is disfavored because of steric clashes.

Ramachandran


Ramachandran

Diagram for

Helices

Both right- andleft-handed heliceslie in regions ofallowedconformations inthe Ramachandrandiagram. However,essentially all helices in proteinsare right-handed.


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Ramachandran Diagram For Strands

The red area

shows thestericallyallowedconformations ofextended, -strand-likestructures



Ejemplos de protenas fibrosas

Queratinas

Colgeno


Alfa - Queratinas

An -Helical Coiled Coil. The two helices windaround one another to form a superhelix. Suchstructures are found in many proteins includingkeratin in hair, quills, claws, and horns.

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Colgeno The structure of a typical collagen

molecule.

(A) A modelof partof a single collagen chain in which each amino acid isrepresented by a sphere. The chain isabout 1000 amino acids long. It isarranged as a left-handed helix, withthree amino acids per turn and withglycine as every third amino acid.Therefore, an chain is composed ofa series of triplet Gly-X-Y sequences,in which X and Y can be any aminoacid (although X is commonly prolineand Y is commonly hydroxyproline).

(B) A model of part of a collagenmolecule in which three chains, eachshown in a different color, are wrappedaround one another to form a triple-stranded helical rod. Glycine is theonly amino acid small enough tooccupy the crowded interior of thetriple helix. Only a short length of themolecule is shown; the entire molecule

is 300 nm long.


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Protenas 2


Protenas globulares: estructuraterciaria, modelos de plegado

La mayora de las protenas estn formadas por ms de undominio

Existe siempre un interior de residuos hidrofbicos y unexterior de residuos hidroflicos.

Las lminas estn generalmente envueltas enestructuras cilndricas.

Existen giros en la cadena polipeptdica para doblar enesquinas o ir de un segmento a uno o viceversa. Tipos

de giros: y . No todas las partes de las protenas globulares son hlices

o lminas , o giros. Existen segmentos conectores oregiones estructuradas irregularmente.


Modelos de plegado

Existen ciertos motivos comunes enprotenas: Todas tienen ms de un dominio Hay un interior hidrofbico y un exterior

hidroflico Lminas beta estn envueltas en estructuras

tipo cilindro Hay giros No todo es hlices alfa, o lm. Beta, tambin

hay segmentos conectores


Dominios de protenas Protein Domains. The cell-surface protein CD4

consists of four similar domains Dominio: regin compacta, plegada localmente,

de la estructura 3


Tipos de

Giros:

Giro tipo

Giro tipo


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Barriles beta


Tipos de plegados de

protenas globulares


Ejemplo deprotena ricaen lminas

beta

Immunoglobulin Fold. Animmunoglobulin domainconsists of apair of-sheets linkedby a disulfide

bond andhydrophobicinteractions.Threehypervariableloops lie at oneend of thestructure.


Qu est sucediendo?


Factores quedeterminan lasestructuras 2 y 3.Desnaturalizacin yagentesdesnaturalizantes.Papel del S-S.

La mayora de lainformacin quedetermina laestructura 3-D deuna protena lalleva la secuenciade aminocidos.

Estructura Nativa Desnaturalizacin Renaturalizacin


Estabilizacin de la estructura 3 a) Interacciones carga-carga b) Puentes de hidrgeno internos. Hay tres

tipos: armazn con armazn, armazn concadena lateral y cadena lateral con cadenalateral.

c) Fuerzas Van der Waals d) Efecto hidrofobo: el enterramineto de los

grupos R hidrofobos en el interior de laprotena produce un aumento de la entropade estabilizacin.

e) Puentes S-S: formados exclusivamentepor Cys


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Estabilizacin por puentes de H


Estructura cuaternariaAsociacin de cadenaspolipeptdicas para formarestructuras especficas demltiples subunidades.

Qu estabiliza la estructura4?

Las mismas interacciones queestabilizan la estruct. 3.


Three-Dimensional Structure of Myoglobin. (A) This ball-and-stick modelshows all nonhydrogen atoms and reveals many interactions between theamino acids. (B) A schematic view shows that the protein consists largely ofa helices. The heme group is shown in black and the iron atom is shown asa purple sphere.

Mioglobina


Hemoglobina


Importanciabiolgica de lahemoglobina


Importanciabiolgica de lahemoglobina

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