ThE PLMATH SENT, A WS LATE! COMPIGQURATION oF

POLTPEPTICE Ceale
By Linus Peclicg ani Fobert 2. Gorey

Gates ant Creliia Leberaterien of Chertetry*
Califernia Institute of Teahrwlegr, Pasadena, Calif.

Secmunteated Maret 3951

For wany veare {% hase bean asaured thst io atlk (ibroin, stretched
heir and anscla, ax! other proteins with the Skeratia structure the
polypeptite ciaiae sre actended to marly their vaxtrvas length, about
3.6 & per residams acd during the last decade it has been eastwued alee
that the chaise fore Lateral hydrogen bonte with afiaeent chatne, which
heve the erpoetite orlewtation, A tydrogen-bonted larer of thie sort ie
repreeented diagrammatically tn igure 1.2+ 2+ 39 4

We have now diesowered that there {¢ another, mather a'ntlar
hrdrogensbonded layer configuration of polypeptide halis, whish differs
fro: that of Figuee 1 in several ways. In the new configuration, + toh
we ghall enll the “leated«sheet configurations the plane formed by the
two chain bow of the a earbor ate ta perpendicular to the plane «f
the ehowt, as «how: in Mpourea 2 am! 3, rater than being solnctident
with {t. In (sta struetere the aueceacive reatéuss in a chair re)
ginllarly oriental, étrecti ng thetz carbon) groups “and Ae intne

incon
ground in the sameway, oo? all of the chaine are ortented in the pane
~ 2 «

way, inwtend of a¢iacect chatne be'ng ov pesed in direction,

Let as came thet a pelyveptide chain with ‘he eenfi guration
intteated dlegrannatioally in Figure 2 te bent fn such « we thet the
planss of the susccssive Saved fora dthodral anglos vise edges are
perpenticular te the plane formed by the axes of the Susttuns (the
lines conmoting euccesaive « earben atom).  t 1s ford that if the
bond dietanees art ben! angles are given the walues that «es have used
in our recent considerations ef protein cenfiguretionsa, tha dihedral
angle hae the walne 106,5% and the vertices! ecacenent of the axis of
each residue te 3.07 4. %t is aleo fount that the carbons] and {nine
grovpe are orlented {mn wuch a way that the, ean form aatisfsetory
hydrogen “ends with correspanding gr-ure in ahaine obtained by lateral
translation. If the lateral tranelatieon ts given the value 2.75 4,
the Hauwless diatancs ta 2.7§ Ay thie le a porvel hydregensbent’ distance.
The HeeH axis ites within 6* of the Nees axis, indicating that a stable
hytrogen bond showld be formed, The csemiinates of atoms for the pleated-
sheet conftguration are given tn Table 1, ant a drawing of the confige
eration {a shown an Figure 3.

Tt 19 to be noted that each teide group in the chein (negloeting
the side chaine) may be deacrthed an obtained froe the preening one
by tha operation off « glide plane of eyemetr’. Fooaune of thing cide
chains of | aniro acid residues are related different] te the structure
vhen attached to one « earbos ates than when attached te the a carbon
ates of en adjacent residue, The nleatel-aheat oonfi curation can ae<
cordingly be deseribed ae invelwing only one kind of giveine residue,

im case thet 1¢ were to be acmimed by a colyrlyeine, ut tue kinds of
aw Dw

residues fer all optiesliy active antre-eetd polymers. These two kinda
differ 1a thet, for the |, configuration, a residues of one kind psints
its 6 carbon stem in the C=r0 direction, and a reeidue of the other
kind points ite £ eben ates in the Mel direction,

Ve have found aceon evidence to support the belief that the pleated«
aheat configuration {s present {n stretched cusele, stretched hair,
festher kerating ani some other Nbrows proteins that have been asetmed
the ‘~keratin structure. These rroteins give mrey diagrars on whieh
there ts a stresg meridional reflection correspending te spacing about
303 hey which {8 2 fow parcent larger than the Mbersaxie diatanoe per
residue for the undistorted rleated sheet, but such emaller than the
value job Ay Sor Cully extended polypeptide chain, tie have notioed
that the pleated sheet oan te subjected, vithut rumtaring the hydregen
bende, to « opnstdoreble distortion, tu such « war an te {oerease the
fibormaxis distenss, This diatertion is effoeted by rotating each
imide group about ite Ge" axis through « omall ancle. The rotation
moves one cf the two 7 pesttions of zach earbon eaten farther fren the
median plane and the othor nearer, and the effective retations for
the two nenserat valent Minds of optiosally active residues are such ae
to permit each to be an | reaidue with ite side chain farther fren the
meiian plane than in the wilisterted strugture, Presunsbiy the van der
Veale repaleton of the side abets ates and the main ehein atoms wrild
be operating in proteins of normal shextoal composition with the pleated»
ahbeet eonfiguration, and this vould eaune sose distertion of the ahaine
lengthening sort, (Tt ts to be noted that tw kinds of pleated sheate

san be constructed of | arinoegeld residues, ef whteh for one the
kan

the deformation that relieves the strain of side-chain van der Waals
repulsion inereases the fibar-exis length, ané for the other 1t de-
oreases it.) Tt might wall ocour that the magnitade of the doforme
tien would be sush as to give the Miber-amis residue length observed
for the f-keratin proteins, about 3,3 A. This deformation resulte
fron a 20° rotation of the imide groupe, vhich gives 3.32 A. ae the
residue length, Geerdinates for the strocture with 20° rotation and
alse for « lese coformed atructure, with 7* retetion, are given itn
Table 1,

The deformed structures require same distortion of the hydrogen
bonds, in thet {f the hydrogen atom {a kept eoplanar with the inide
group the Ho dirwetion deviates from the 5++s0 axis by an angle
eonewhat greater than the distorting angle of rotation. The nature of
the distertion is auch, however, as to suggest that not sugh strain
energy ie involved. Let us consider the effect on the atabiiity of the
imide group of moving the hydrogen atom onto (or nearly: onte) the
HeerQ axis, “oO would keep the hydrogen atow nearly in a plane
normal to the Planes that is, it involves sovring the hyregen
atom towarts one of the tetrahedral corners of the nitrogen atom. If
the nitrogen atom were forming a pure double bend with the carbonyl
oarbon C! there wold be strong resistance to this cotien of the hytre-
gen atom, ‘owewer, it ferns a bond with about one-half dowble-boni
———— ee charanton oorrespeniing to the ros-
onance = ==3! . or

c aps ra or

-~

j and for the second of
« 5 o

the structures the tetrahedral position for the hydrogen atom would be
the norsal one, vhereas for the first the planar position is stable,
docordingly we would predict thet thie rotational distortion of the
pleated sheet would not invelwe so wuch strain ae if the bonds vere
double bonds,

Ne may now ask to what extent distortion of the dnide group fre
the planer eonfiguration, through rotation of the two ends "Sarat
eae tn eppestite directions sbout the N=<0' exis, night be ex
pected een, The strain energy of this distortion, which is essen~
tially aleo the strain energy of distortion of the hydrogen ator aut of
the plane, can be estimeted in the fellewing way. With the athedral
angle formed by the planes of the two end groups, the inide resonance
energy nay be taken equal to oh ain” (5-2), ant the strain overey
to gain” 5. the factor 4 is the inide resonance energy for the planar
configuration, This nay be estimated as about 30 heal mole”!, (The
experimental value for the carboxylate ion, in which each of the two
C—O bonds hae 50 pereent doublesbond character, 1s 36 keal mole”, and
gomevhat snaller values are found for axides, osters, and related aub-
etences.”) We thon Fed abewt Of Weal note” strein energy for 10°
distortion of the Exide group, 4.8 keal mole”! for 2° distortion, end
80 on, and we may prediet that distortions 20 largs as 20° might well
ecour, in structures in whieh these Cistortions would relieve a larger
strain, but that in goneral the polypeptide chain would avold structures
iwrolving such strains, In any oase, ve would expect the distortion to
be divided between the imide residue and the hydrogen bend. In calaul-
ating the coordinates of Table 1 ve have not taken aceount of these ¢is-
tertions.
= 6 =

The Aiscuseion of the pleated sheet in febevatin and other pre-
teine will be presented in following papers. in this discussion wa
make wie of the meray seattering form factor for the sheet. The form
factor, ealeulated for re(iections from planes parallel te the nedtan
plane ef the undistorted sheet, is for eonventent leter reference given
hare, in Figure 45 as exleulated from the acustion F = 1; ove (2try sin 6h).
The sum hae doen taken ever the atoms of one reetéue of the undisterted
wtrueture, including alee « / carbon atoms with y © 2ehy the tj values
given in the Internation] Tables for (Gryatal Structure; feternination +
having been used,

Thie investigation wan aided by a grant from The Heekefaller
Foundation, The National Foundation for Infantile Paralreis, and The
Batted States Public Health Service,
Geerdinates of Atoms in the Polypeptide Fleated«shest Configumtion

0.00
236
6.53
1.74
0.00
~6436
0.53
1.7%
6.00

1.45
6.30
+0 ,28
Oedh
e1e5
Be
28
Odd

0,00
Leds
1.9
1.73
3.07
res]
4.98
bat
6.14

isla i.

7° Retation

0.00
0,36
6.53
1.72
0.00
0,36
0453
1.72
0,00

1.09
O46
0.32
31
~1.09
90.39
0.22
04
2.09

0.08
1.17
2.96
1.75
3035
42
5al2
4e95
6.30

20° Rotation

0.00
436
0.50
1.63
0400
90034
0.%
1.63
0.00

0.96
0.35
~0.40
“0464
96
0.14

0.39
0.96

0.00
2.29
1.98
1.58
3.32
edd
5049
5.50
6.64
*Contetietion Me.
Tastoury, <. Tos Donnas Zeguday Sag-s 2B 193 (1993).
*wageine, M. Tne ds See. Samo de 407 (1996)) Gham. Bexes Seo
195 (1943).
*Pautings Les d+ due Gham Sages Gite 2643 (2940).
‘yotmar, Way art Ploken, L. B. Rey Hgly. Shin Agha, Zi» 538 (1942).
Syautings Ley The Nature of the Ghenioa) Bond, Cornel) Univers! ty
Press, ithaca, ew York, 2979,
é “06 »
{ = | | =
Su Sg NN GON
om a
a | I ce |
z 9 -
6 . 9
es ok 8 US
a “iy or S57 No” So
| fe { | fa
= o>
6 = Oo
i « 7 7 ¢
Nog ON NGOS ~
= | = |
fe | | 2
H 8 .

> Diagrematio representetion of
r strusture of palypert .

Fige 1.

hydrogen

ide chains, with alternate
\
CHR CHR CHR
\ \ \
— =
HW / “<0 HW” ~~ O H% a
\ \ \
CHR CHR CHR.
\ \ \
—— VS a
Hf =o. HW,” O AH f. =O
\
CHR CHR CHR
\ \. \.
\ \ \
CHR CHR CHR
\ \
= = ye
\ \ \
CHR CHR CHR
\ \ \

Figs 26 Dingrasatie representation of a
ne nded layer structure of polyreptide chains,
with nll cheins sintlerty oriented ( the pleated sheet).

  
 

Pigereties 2F petite, remeomnting the plentat_shact ccm
 

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| |
30 —
F
20 a
lob ~
ol 1 | | | l |
0.05 O10 O15 020 025 030

sin 8/