Tài liệu Báo cáo khoa học: Multiple enzymic activities of human milk lactoferrin ppt

Multiple enzymic activities of human milk lactoferrin

Tat’yana G. Kanyshkova1

, Svetlana E. Babina2

, Dmitry V. Semenov1

, Natal’ya Isaeva3

,

Alexander V. Vlassov1

, Kirill N. Neustroev4

, Anna A. Kul’minskaya4

, Valentina N. Buneva1

and Georgy A. Nevinsky1

1

Novosibirsk Institute of Bioorganic Chemistry, Siberian Division of Russian Academy of Sciences, Novosibirsk, Russia;

2

Novosibirsk State University, Novosibirsk, Russia; 3

Institute of Cytology and Genetics, Siberian Division of the

Russian Academy of Sciences, Novosibirsk, Russia; 4

Petersburg Nuclear Physics Institute of Russian Academy of Sciences,

St Peterburg, Russia

Lactoferrin (LF) is a Fe3+-binding glycoprotein, first

recognized in milk and then in other human epithelial

secretions and barrier fluids. Many different functions have

been attributed to LF, including protection from iron￾induced lipid peroxidation, immunomodulation and cell

growthregulation, DNA binding, and transcriptional acti￾vation. Its physiological role is still unclear, but it has been

suggested to be responsible for primary defense against

microbial and viral infection. We present evidence that

different subfractions of purified human milk LF possess

five different enzyme activities: DNase, RNase, ATPase,

phosphatase, and malto-oligosaccharide hydrolysis. LF is

the predominant source of these activities in human milk.

Some of its catalytically active subfractions are cytotoxic and

induce apoptosis. The discovery that LF possesses these

activities may help to elucidate its many physiological

functions, including its protective role against microbial and

viral infection.

Keywords: enzymic activities; human milk; lactoferrin;

protection.

Lactoferrin (LF) is a single polypeptide chain of 76–80 kDa,

containing two lobes [1], eachof whichbinds one Fe3+ ion

and contains one glycan chain [2]. It was first recognized

in milk and then in other human epithelial secretions and

barrier body fluids [3–6]. Many different functions have

been attributed to LF, including protection from iron￾induced lipid peroxidation, immunomodulation and cell

growthregulation [6,7], DNA binding [6], RNA hydrolysis

[8,9], and transcriptional activation of specific DNA

sequences [10,11]. It is a potent activator of natural killer

cells [12] and may have an antitumor role [7,13], an activity

that is independent of iron. LF also influences granulo￾poiesis [14], antibody-dependent cytotoxicity [15], cytokine

production [16], and growthof some cells in vitro [17]. The

physiological role of LF and the mechanisms underlying

these activities are still unclear, but it has been suggested to

be responsible for primary defense against microbial and

viral infection [3,5]. LF is a protein of the acute phase; the

highest concentration is usually detected in the inflamma￾tory nidus. It is detected in the blood of newborn babies

several hours after feeding, and can readily penetrate any

cell and nuclear membrane [18]. Owing to its antiviral and

antimicrobial activities, LF increases the passive immunity

of newborns. It was initially suggested that the antimicro￾bial properties of LF may be attributed to its iron-binding

capacity; removal of iron from the microbial environment

is an important defense mechanism as it is needed for the

proliferation of microflora [19]. Many micro-organisms

express surface receptors for LF and it may show different

iron-independent antimicrobial and antiviral properties

[20,21], the mechanisms of which are still a matter of

debate.

We have proposed that, as LF is a relatively small

protein, its polyfunctional properties may result from its

existence in several oligomeric forms that have different

activities, and that its oligomerization and dissociation are

under the control of specific ligands such as ATP [22,23].

In support of this idea, we have shown recently that LF

possesses an ATP-binding site and that interaction of the

protein withATP leads to changes in its interaction with

polysaccharides, DNA and proteins [23]. We have further

demonstrated that LF possesses two DNA-binding sites,

whichinteract withspecific and nonspecific DNAs in an

antico-operative manner and may coincide or overlap with

the known polyanion-binding and antimicrobial domains of

the protein [24].

Here we show that this extremely polyfunctional protein

possesses five enzyme activities (DNase, RNase, ATPase,

phosphatase, and malto-oligosaccharide hydrolysis). The

RNA-hydrolyzing and DNA-hydrolyzing subfractions of

LF may contribute to its protective role through hydrolysis

of viral and bacterial nucleic acids. In addition, we show

that some catalytic forms of LF are cytotoxic and

Correspondence to G. A. Nevinsky, Laboratory of Repair Enzymes,

Novosibirsk Institute of Bioorganic Chemistry, 8, Lavrentieva Ave.,

630090, Novosibirsk, Russia.

Fax: 007 3832 333677, Tel.: 007 3832 396226,

E-mail: [email protected]

Abbreviations: LF, human milk lactoferrin; EPS, 4-nitrophenyl

4,6-O-ethylidene-a-D-maltoheptaoside.

(Received 23 January 2003, revised 13 May 2003,

accepted 11 June 2003)

Eur. J. Biochem. 270, 3353–3361 (2003)
FEBS 2003 doi:10.1046/j.1432-1033.2003.03715.x