Closest packing of two-stranded coiled-coils as a model for the collagen fibril

Vol. 64, No. 4,1975

BIOCHEMICAL

AND BIOPHYSICAL RESEARCH COMMUNICATIONS

CLOSEST PACKING OF TWO-STRANDED COILED-COILS FOR THE COLLAGEN FIBRIL John Woodhead-Gallowayl, David W.L. and John S. Wray3

AS A MODEL

Hukins2

2 Departments of Rheumatology' and Medical Biophysics University of Manchester, Stopford Building, Manchester Ml3 9PT and Institute of Biophysics3, Aarhus University, Denmark.

Received

April

24,1975

We propose that in the collagen fibril, the trip e-helical Summary molecules form two-stranded coiled-coils of period 5 x 670 . Coiledcoils are packed on a tetragonal lattice and are axially staggered with ten in the unit cell (observed side 558) so that it carries the 6702 periodicity of the fibril. When nearest neighbours have opposing supercoil hands, the observed tetragonal lattice represents closest packing of two-stranded coiled-coils. This proposal is consistent with the row line spacings measured from the low angle X-ray diffraction pattern of tendon and explains the systematic absences and the two undisputed equatorial reflections. Unlike explanations for the diffraction pattern which invoke a five-stranded microfibril, our interpretation is consistent with its equatorial intensity distribution. Introduction that

Electron

in axial

referred

projection

to as D).

helical

which

to the axis

by integral numbers

the This

molecules,

parallel

microscopy collagen

are

of D.

allowable

number.

parallel

there

alignment

could

be extended

X-ray

spacings

reflections

were

Within

X-ray

dimensions

must

which

deviations

from rat indicate

tail that

(1)

is the minimum from

exact

suggestion

have been discussed

which

be equal

Hodge and Petruska

Hodge and Petruska's

patterns region

to one another

there

displacements

in which

triple-

approximately

respect

of possible

diffraction

in the equatorial

with

show

of 67051. (usually by the

aligned

one D period

distinct

and the ways three

being

displacements.

five

diffraction

has a period

axially

The significance

into

X-ray

can be explained

4.4D long,

of each of the different that

fibril

observation

and displaced

multiples

suggested

and low-angle

(2,3) .

elsewhere tendon the

fibril

show also

Vol. 64, No. 4, 1975

possesses

order (4) .

lateral

indexing

scheme for

reflections

Table

in the

side

same as that

reflections and in the expected

odd.

This

part

in the original

near

the equator,

which

show the

original

discussion

was not

row lines,

which

equatorial

components,

projected must

we have

1).

is

True

for

these

unit

which

h + k is

systematic are made shows that

cell

of side

The unit

as the whole smaller

even the

observations

axis.

the

all

h + k is

is more

a simpler

data (4)

a/h0

fibril; cell

a/&

cell as in

of side

unit

packing

the

the

a/J2

(4,2),

and

side

(3,1,0)

down the

fibril model

than and

axis

coiled-coil

1238

that

true others

the projected

lattice

the

not

have

structure

Since

contains but

from

two

the

a/42.

(4,2,0)

cell

is

certain

derive so that

Only

clearly

be absolutely

axis,

unit

a two-stranded

(3,l)

reflections

cell

equatorial

models (4,5) .

we cannot

the true

Our proposed

show a true

by earlier

as the

equatorial

i.e.

Molecular

is

few row lines

explained

indexed

are

when projected

unit

fits

to the fibril

identical

elementary

those

reflections

of the fibril

although

reflections cell

are

almost

reflections)

and weak reflections

very

adequately

have an even smaller

jected

(5,0)

of absent almost

that

perpendicular

equatorial

such that

to the

appear

version

is

periodicity.

reflection

(Table

(out

same D periodicity

The observation

do not

(h,k)

these

8, which

Since

of the X-ray

this

55.0

scheme.

to the direction

must

indices

and strong

indexing

being

an

scheme which

In our modified

do not

of molecules

contents

on which of this

cell

proposed.

of absent

near

carries

tetragonal

the pattern

the arrangement

have proposed

row lines

of the pattern

row lines

than

also

a of the

pattern

when viewed

equatorial

are not weak have

inner

only

and Parry(5)

1 shows a modification

originally

that

AND BIOPHYSICAL RESEARCH COMMUNICATIONS

Miller

the near

lie.

results the

BIOCHEMICAL

side

the only of this

10 objects

clear pro-

which

are

otherwise.

shown in Figures of collagen

1 and 2. molecules

The with

BIOCHEMICAL

Vol. 64, No. 4,1975

Table

1.

Observed

and

calculated

AND BIOPHYSICAL RESEARCH COMMUNICATIONS

row

line

spacings'

Miller

Observed

(i-1)2

o-l (A )

Calculated

Intensity

2'3

--h k

and

Calculated

Parry

scheme2

(2-l)

h-- k

.026

.026

s

11

.026

11

.0384

.'036

w

20

.037

20

.041

.041

w

21

.041

21

.053

.052

ms

22

,052

22

.0574

.058

ms

31

.058

31

.064

VW

.067

.066

w

32

.066

32

.073

.073

vs

40

.074

40

.075

.077

VS

33

.076

41

.079 495

.081

"S

42

.078

33

.082

42

.082 .088

VW .091

w

1 50 43

1. 2. 3. 4. 5.

.097

.098

52

.099

52

.1044

,103

44

.104

44

.116

.115

62

.116

62

.123

.122

63

.123

63

.139

.138

7 3

.140

7 3

.147

.146

80

.147

80

.159

.156

75

.156

66

The overall agreement between observed and calculated spacings is reasonable but discrepancies as high as 2.7% do exist in individual cases. Taken from Reference 5. Where intensities are very strong (vs), strong (s), moderately strong (ms), weak (w) and very weak (VW). Row lines with an apparent equatorial component. Only the (3,l) and (4,2) row lines clearly show an equatorial reflection. This spacing may be an underestimate because of overlap by a diffraction maximum arising from liquid-like disorder (9,12).

1239

Vol. 64, No. 4, 1975

BIOCHEMICAL

AND BIOPHYSICAL RESEARCH COMMUNICATIONS

:. /I :

OVERLAP

LONG

5 x67OK

OVERLAP

i

i

~

Figure 1. Diagram (a) and drawing (b) of the two-stranded coiledcoil showing the 5 x 670x periodicity. Notice that there are two gap regions and one long and one short overlap per 5 x 6702 period.

a period

of 5 D (Figure

stranded

microfibril

diffraction

the cell

suitably

displaced

to carry

this

of true

tetragonal

must

This

.

For

unit

could

reflections

This

has the advantage

lattice

is what

with

be packed

described

we would

consists

cell

interpretation

equatorial model

(n is If the

solution

true

This

contents

direction.

the simplest

II apart.

cell

5n coiled-coils

in the axial

object

than

been used to interpret

the unit

contain

the coiled-coils

= 17.4

is a much smaller

has also

and a larger,

tetragonal

55/JlO

(4)

period

5 coiled-coils is

which

pattern

periodic

1).

over expect

1240

the X-ray

to be strictly

D

any positive smaller

10.

Since

supported

integer)

cell

of a small

as in Figure is

the five

is cell

also with

the unit Za,

by the pattern

above. others

that

in order

the observed to achieve

closest

cell

Vol. 64, No. 4,1975

BIOCHEMICAL

AND BIOPHYSICAL RESEARCH COMMUNICATIONS

Possible arrangement of two-stranded coiled-coils with Figure 2. cell of side a/42. the unit cell of side a = 55w and the sm ller each of period 5 x 670 8 , are arranged so that each The coiled-coils, displaced relative to it by 1 x 670,2 x 670 is surrounded by fo r others the five 3 X 670 and 4 x 670 P . The numbers 1 to 5 represent distinct axial displacements of the Hodge and Petruska suggestion (1). In (b) the supercoil has rotated through 45O from the position in (a); here the lattice is equivalent to tetragonal packing of molecules. The true Adjacent supercoils are turning in opposite directions. The circles unit cell and the smaller unit cell are marked. representing molecules in (a) are drawn slightly smaller than in (b) for the sake of clarity only; the correct size is shown in (b).

packing

of two-stranded

two-stranded

coiled-coils

molecular

radius)

once that if

adjacent

closest

(6)

coiled-coils

by packing

with

opposite

supercoil

r = 38.9//40

= 6.15

8 for

the collagen

coiled-coils

have

approach

apart

is achieved

The closest

.

is

(2+42)r

the

which

1241

lead

them 2/.2r

between

(where

This

hands.

same supercoil would

packing

r is the

tells

us at

molecule.

In contrast

hand,

distance

to a smaller

their

radius

for

of the

Vol. 64, No. 4, 1975

collagen

BIOCHEMICAL

molecule,

coiled-coils

than

model

have opposing

represents

the closest ---

The closest

packing

a tetragonal

cell

siderations

the

but

which

are

possible

test

is

of these

diffuse

On the

is

a spacing

which

background. disorder order

angle.

not These

in con-

u-helical

which

have each of

the unit

comparison

cell

of this

carries kind

is

pattern

consists is

the Fourier

difficult

This

cannot transform

pattern

with

that

value

where

the diffuse could

also

of r (9) .

1242

on

intensities and

yet.

of a two-stranded

reaches intensity

the

background

be resolved

converted

intensity)

(8) but it this

pattern.

superimposed

strong

coiled-coil

x = 2ard.

into

For molecules

of the observed

in the lattice of molecules

of this

functions.

suggests

the

and observed

to measure

to Jo(x).Jl(x)/x,

(predicted

with

diffraction

of reflections

because

on the diffraction

the position

X-ray

of the predicted

It

proportional

is consistent

(7) .

reflections

equator

our model

low angle

on the row lines

transform is

others

An arrangement

in the

and Jo and J 1 are Bessel squared

ropes.

same results

of those

so that

shown that

confidently

reflections

approximately

by four

2).

background.

of the reflections

is

the

a 71.8'

packing

displacements,

We have

The diffraction

because

two-stranded

2.

A more critical

a strong

with

adjacent

arrangement

supercoiled are

If

coiled-coils.

surrounded

of the reflections

intensities

of 5 8.

tetragonal

hands

to the

(see paragraph

intensities

positions

is

the

cell

two-stranded

suggest,

-for

two supercoil

relative

shown in Figure X-ray

possible

relevant

also

the D periodicity

hands

in a monoclinic

Each coiled-coil the four

would

supercoil

are possibly

proteins

building

packing if

AND BIOPHYSICAL RESEARCH COMMUNICATIONS

8 ngstrBm

with

r = 6.15

Here d units 8 the

a maximum when d = 13 8 maximum in the diffuse

scatter arise

could from

arise

liquid-like

from dis-

Vol. 64, No. 4, 1975

BIOCHEMICAL

Since

we do not

coiled-coil,

of the

intensities

1 : 1.3 which

five-stranded very

agrees

strong

(4,2,0)

Therefore,

as first

compatible

with

Conclusions stranded

reflection

but

that implies

differences

in the

packing for

the

energies

true

scheme with

the triple-helical

cell) all

weak

the

that

(ratio

the

- 1 : 10m3).

intensities

fibril

are

each one has four 2 x 670,

gain

near

(This

to ----the closest

in free

energy

to unit

carrying

rise

cells

the 670 8 period.

features, molecule,

which is

of twoare

may seem unlikely, packing

implies

of the

small

hand.)

Tetragonal

of sides

38.9

A possible a radius

shown in Figure

2.

discussion, in whose

3. 4. 5.

J.A. (1963) in "Aspects of Protein Hedge, A.J. and Petruska, Structure", Ramachandran, G.N. (ed.), pp. 289-300, Academic Press, New York. Chapman, J.A. (1966) in "Principles of Biomolecular Organisation", Wolstenholme, G.E.W. and O'Connor, M. (eds.), pp. 129-130, Churchill, London. Chapman, J.A. to be published. Miller, A. and Wray, J.S. (1971) Nature, 230, 437-439. Miller, A. and Parry, D.A.D. (1973) J. Mol. Biol. 75, 441-447.

1243

51

detailed

of 6.15

References.

2.

arranged

neighbours

outweighs

can give

We thank Dr. J.A. Chapman for Acknowledgements. Dr. G. Dodson for encouragement and Dr. A. Miller laboratory we first worked on collagen.

1.

broadly

3 x 670 and 4 x 670 8.

hands.

leads

consists

The coiled-coils

of different

collagen

reflections

predicts

of supercoils

these

(4,2,0)

that

In contrast,

(4,lO)

5 x 670 8.

by 670,

of the coiled-coils g (the

and

observation.

the collagen

arrangement that

of the

we are proposing.

have opposing

this

coiled-coils

and 55.0

to it

of the

above we predict

(3,1,O)

be relatively

that

so that

respect

given

collagen

of the kind

lattice

coiled-coils

the fact

for

of period

Neighbouring

with

will

We have proposed

with

strong

pitch

intensities

by Burge 01) , the X-ray

noted

a model

on a tetragonal

packing

model

coiled-coils

staggered

reasonably

of the

the

the transform

of the

microfibril

estimate

to considering

Using

reflections.

the ratio is

have an accurate

we are restricted

equatorial

AND BIOPHYSICAL RESEARCH COMMUNICATIONS

2

Vol. 64, No. 4, 1975

6. 7. 8. 9. 10. 11.

12.

BIOCHEMICAL

AND BIOPHYSICAL RESEARCH COMMUNICATIONS

Woodhead-Galloway, J. (1975) J. Appl. Crystallogr. submitted for publication. Hukins, D.W.L. (1975) in nStructure of Fibrous Biopolymers", Proceedings of the 1974 Colston Symposium, Univ. of Bristol, Butter-worth, London, in press. Arnott, S. (1973) Trans. Amer. Crystallogr. Assoc. 9, 31-56. Machin, P.A. and Woodhead-Galloway, J. to be published. Smith, J.W. (1968) Nature, 219, 157-158. Burge, R.E. (1965) in "Structure and Function of Connective and Skeletal TissueV, Fitton Jackson, S., Harkness, R.D., Partridge, S.M. and Tristsm, G.R. (eds.), pp.2-7,Butterworth, London. Hosemann, R., Dreissig, W. and Nemetschek, T. (1974) J.Mol. Biol. 83, 275-280.

1244