The molecular structure of glutamine synthetase from anacystis nidulans as studied by electron microscopy

Micron and Microscopica Acta, Vol. 18, No. 3, pp. 225—226, 1987 Printed in Great Britain

0739—6260/87 $3.00+0.00

© 1987 Pergamon Journals Ltd.

THE MOLECULAR STRUCTURE OF GLIJTAMINE SYNTHE~IASE FROM ANACYSTIS NIDULANS AS STUDIED BY ELECTRON MICROSCOPY

L.Leurentop, F.J.Florencio(l) and J—P.Verbelen

University of Antwerpen,U.I.A. ,Department of Biology,Universiteitsplein 1, 26l0—Wilrijk, Belgium (1)

university of Sevilla, Department of

Biochemistry,

Apartado

1.095,

41080 Sevilla, Spain

The structure

OS

of

(glutarnine synthetase) of Escherichia coli has been

studied thouroughly by electron microscopy (See Kessel et al. ,1980). It is clear that the 600.000 MW two eclipsed Here buffer

is composed of 12 subunits arranged in

hexagons.

we

Anacystis

complex

report

on

nidulans.

solution

a

study

The

of

the structure

of the GS molecules of

enzyme was purified and brought and

(10mM)

then

diluted

for

an

in

a

optimal

diluted electron

microscopic observation. A drop of solution was applied to a specimen grid coated with a thin

carbon

preparations

studied

were

film

and

contrasted with uranyl acetate. The

generally with

a

Jeol

1200

CX;

critical

micrographs were recorded with a Jeol 200 CX at low dose. On

the

preparations

two

majority of the molecules was (Fig.l).

molecular shapes could be discerned. The rather

large

and

had

a

circular

shape

The remaining fraction consisted of smaller molecules which later

were identified

as

hexagonal-circular reinforcement establish of six

subunits of the large form. This latter had roughly a shape with a

diameter

of

about 15 nm. Applying image

(Fig.2) and averaging techniques (Fig.3) we

the polymeric nature of the structure. smaller

units,

arranged in a circular

could

clearly

The hexagon is a

complex

pattern,

leaving a central

hole in the middle of the polymeric structure.

The subunits seem to have a

certain

handedness as they have

versus

global

circular—hexagonal

in profile

(Fig.l).

symmetry

structure.

~R~o types

that the complex structure

no

a radius of the the

Sometimes molecules can be observed

of images can then be recorded. They show

is composed of two similar hexagons attached to

each other so that they are eclipsed in surface view. The

molecular

described

structures

observed

for GS of Escherichia

are very

coli,

a

similar

to

nonphotosynthetic

the

shapes

procaryoot.

References Kessel M. ,Frank J.and Goldfarb W. structure

(1980)

Journal

14:405—422 225

of

Supramolecular

226

L. Leurentop et al.

Fig.l. Purifi g utatamine synt etase iso at rom acystis ni u ans, negatively stained with 1% uranyl acetate.(Scale bar = 3Onm).

Fig.2. Image processing of GS molecules by optical superposition. Picture (a) shows the original electron micrograph of a single enzyme molecule. 6-fold rotation by 60 (e) gives a clear reinforcement of intensities with a periodicity of 6. Other periodicities (360.n ,with n=2(b),3(c),4(d) and 8(f)),served as controls. As expected also 2— and 3—fold rotation gave an intensification.Scale bar = 5nm.

Fig.3. Image processing of OS molecules by computer. Picture (a) shows again the original electron micrograph.The 6-fold rotation by 60 gave a clear reinforcement of intensities with a periodicity of six (d). These results state the conclusion taken after image ~rocessing by optical superposition.Scale bar = l5nm.