Tài liệu Báo cáo khoa học: Mapping the functional domain of the prion protein docx

Mapping the functional domain of the prion protein

Taian Cui1

, Maki Daniels2

, Boon Seng Wong3

, Ruliang Li3

, Man-Sun Sy3

, Judyth Sassoon1

and David R. Brown1,2

1

Department of Biology and Biochemistry, University of Bath, UK; 2

Department of Biochemistry, Cambridge University, UK; 3

Institute of Pathology, Case Western Reserve University School of Medicine, Cleveland, Ohio, USA

Prion diseases such as Creutzfeldt–Jakob disease are pos￾sibly caused by the conversion of a normal cellular glyco￾protein, the prion protein (PrPc

) into an abnormal isoform

(PrPSc). The process that causes this conversion is unknown,

but to understand it requires a detailed insight into the

normal activity of PrPc

. It has become accepted from results

of numerous studies that PrPc is a Cu-binding protein and

that its normal function requires Cu. Further work has

suggested that PrPc is an antioxidant with an activity like

that of a superoxide dismutase. We have shown in this

investigation that this activity is optimal for the whole

protein and that deletion of parts of the protein reduce or

abolish this activity. The protein therefore contains an active

domain requiring certain regions such as the Cu-binding

octameric repeat region and the hydrophobic core. These

regions show high evolutionary conservation fitting with

the idea that they are important to the active domain of

the protein.

Keywords: copper; Creutzfeldt–Jakob disease; oxidative

stress; scrapie; superoxide dismutase.

Neurodegenerative diseases are a major threat to human

health. One group of disease termed prion diseases [1,2]

make up a small percentage of all human neurodegenerative

diseases. Prion diseases have become a major concern

because of the possibility that one particular from, variant

Creutzfeldt–Jacob disease (vCJD), might arise through

transmission of an animal disease, such as bovine spongi￾form encephalopathy [3], to humans [4]. Other prion

diseases include the sheep disease scrapie [5] and inherited

forms such as Gerstmann–Stra¨ussler–Scheinker syndrome

[6]. All of these disease are linked together because of the

deposition of an abnormal, protease-resistant isoform of the

prion protein in brains of individuals with these diseases.

This abnormal form of the protein (PrPSc) is also suggested

to be the infectious agent in the disease on the basis of

infection studies [2].

PrPSc is generated from the normal cellular isoform of the

prion protein (PrPc

) which is present in the brain as a cell

surface glycoprotein [7]. Each form has distinct properties

[8]. Therefore understanding the basis of prion disease

revolves around understanding how the normal protein is

converted to the abnormal isoform. This conversion

involves a switch in conformation from a structure rich in

a helices to one rich in b-sheet [9]. Although there have been

many studies with PrPSc the study of PrPc has been limited

until recently. As an evolutionarily conserved glycoprotein

[10] it has been postulated that PrPc has an important

function. Nevertheless, knockout mice for PrPc show no

gross changes in terms of development or behaviour [11]

but cannot be infected with mouse-passaged scrapie [12]. In

contrast to this biochemical and cell biological studies have

suggest that PrP-knockout mice have compromised cellular

resistance to oxidative stress [13,14].

The first clue to the molecular function of PrPc came from

studies that show PrPc to be a Cu-binding protein [15–20].

The main Cu-binding site of the protein was shown to be

within a conserved octameric repeat region, rich in histidine,

located in the N terminus [10]. PrPc binds up to four atoms

of Cu at these sites with a possible fifth binding site located

elsewhere in the molecule [16,18,21]. Cellular expression of

PrPc also facilitates Cu uptake by neurones [22] and

increased extracellular Cu causes an increased turnover of

PrPc [23]. Binding of Cu to the protein influences its ability

to interact with other proteins such as plasminogen [24] and

glycosaminoglycans [25].

Knockout of PrPc causes a decrease in cellular resistance

of neurones to oxidative stress [13,14,26]. This has lead to

suggestions that PrPc might be an antioxidant. Immuno￾depletion of PrPc from the brain extracts leads to a

reduction in superoxide dismutase (SOD) activity within

the extract [27]. Studies with both recombinant protein and

native protein purified from the brains of mice suggest that

PrPc can act as a SOD [17,28]. This activity is high and

requires specific binding of Cu to the octameric repeats.

Binding of Cu elsewhere in the protein, or Cu simply to a

peptide based on the octameric repeats does not result in

this activity [28]. Cellular resistance to oxidative stress is

influenced by the PrPc protein and the amount of Cu bound

to it [17]. Allelic differences in mouse PrPc have also been

shown to influence the level of the activity of the protein, as

protein with the sequence of the mouse
b allele is more

Correspondence to D. R. Brown, Department of Biology and Bio￾chemistry, University of Bath, Calverton Down, Bath, BA2 7AY, UK.

Fax: +44 1225 826779, Tel.:+44 1225 323133,

E-mail: [email protected]

Abbreviations: CJD, Creutzfeldt–Jacob disease; vCJD, variant

Creutzfeldt–Jacob disease; PrPc

, prion protein; PrPSc, abnormal

isoform of prion protein; rPrP, recombinant mouse prion protein;

SOD, superoxide dismutase.

(Received 28 April 2003, revised 5 June 2003, accepted 11 June 2003)

Eur. J. Biochem. 270, 3368–3376 (2003)
FEBS 2003 doi:10.1046/j.1432-1033.2003.03717.x