隨著生命科學(xué)的不斷發(fā)展，乳鐵蛋白的抗菌機(jī)制被廣泛地運(yùn)用到生物制藥、美容美妝、保健食品、醫(yī)療醫(yī)美等各個(gè)產(chǎn)業(yè)。本次小編將匯總多篇文獻(xiàn)證據(jù)為大家盤(pán)點(diǎn)乳鐵蛋白抗菌機(jī)制。

1.乳鐵蛋白的結(jié)構(gòu)

乳鐵蛋白是一個(gè)由約700個(gè)氨基酸組成的80kDa糖基化蛋白，在物種間具有高度同源性。乳鐵蛋白擁有兩個(gè)對(duì)稱的同源球狀域：N-環(huán)和C-環(huán);N-環(huán)對(duì)應(yīng)于肽鏈中的第1-333個(gè)氨基酸殘基，而C-環(huán)與第345-692個(gè)氨基酸殘基對(duì)應(yīng)，這兩個(gè)域的兩端由一段短鏈α-螺旋相連接。每個(gè)環(huán)有兩個(gè)子域(亞域)：N1、N2和C1、C2 組成，并分別包含一個(gè)鐵結(jié)合位點(diǎn)和一個(gè)糖基化位點(diǎn) ^[1]。

乳鐵蛋白三維結(jié)構(gòu)^[2]

乳鐵蛋白能結(jié)合多種金屬離子：Fe²⁺、Fe³⁺、Cu²⁺、Zn²⁺和Mn²⁺等，它主要以兩種形式存在：富含鐵形式的holo-lactoferrin和不含鐵形式的apo-lactoferrin。兩者有不同的三級(jí)結(jié)構(gòu)：apo-lactoferrin的特點(diǎn)是有一個(gè)“開(kāi)放式”的N-環(huán)和一個(gè)“封閉式”的C-環(huán)，而holo-lactoferrin兩個(gè)環(huán)都是“封閉式”的^[3]。

正是由于乳鐵蛋白可以可逆結(jié)合鐵離子的特性，奠定了其抗菌作用機(jī)制的基礎(chǔ)。

2.乳鐵蛋白抗細(xì)菌機(jī)制

大量研究者研究了乳鐵蛋白對(duì)于革蘭氏陽(yáng)性菌(G⁺)和革蘭氏陰性菌(G^-)在體內(nèi)和體外的抑菌性能和機(jī)制，簡(jiǎn)單匯總?cè)缦拢?/p>

表1 乳鐵蛋白對(duì)常見(jiàn)菌株的抑菌機(jī)制^[2]

乳鐵蛋白發(fā)揮抗菌活性的作用機(jī)制可以概括如下：

2.1 鐵隔離或鐵剝奪作用：

鐵離子是大多數(shù)細(xì)菌生長(zhǎng)所必需的營(yíng)養(yǎng)物質(zhì)，參與了許多重要的生物學(xué)過(guò)程。乳鐵蛋白具有較高的鐵離子親和性，可以通過(guò)螯合鐵離子與需要鐵離子的細(xì)菌競(jìng)爭(zhēng)性結(jié)合鐵，將鐵離子從細(xì)菌病原體中隔離出來(lái)，限制細(xì)菌在感染部位對(duì)這種營(yíng)養(yǎng)物質(zhì)的使用，抑制細(xì)菌的生長(zhǎng)，并下調(diào)其毒力因子的表達(dá)。

2.2 改變細(xì)菌細(xì)胞膜的通透性：

乳鐵蛋白能夠與細(xì)菌表面分子非特異性結(jié)合，封閉細(xì)菌細(xì)胞膜上的通道位點(diǎn)，阻斷營(yíng)養(yǎng)物質(zhì)和細(xì)菌蛋白的運(yùn)送，從而抑制細(xì)菌的合成、代謝。脂多糖(LPS)為革蘭氏陰性菌細(xì)胞外膜的主要成分，乳鐵蛋白通過(guò)與脂多糖的相互作用破壞革蘭氏陰性菌的外膜，改變細(xì)胞膜的通透性^[29]，達(dá)到直接殺菌作用;乳鐵蛋白N-端帶正電荷也可以通過(guò)阻止LPS與細(xì)菌陽(yáng)離子(Ca²⁺和Mg²⁺)之間的相互作用，有效干擾大腸桿菌的聚集性增殖^[30]。

2.3 抑制細(xì)菌粘附或定植：

乳鐵蛋白的N-末端具有絲氨酸蛋白酶活性，能有效地從流感嗜血桿菌(G^-)外膜中提取IgA1蛋白酶前蛋白，還能特異性地降解Hap黏附素并阻斷Hap介導(dǎo)的黏附，從而防止流感嗜血桿菌的定植^[31]。乳鐵蛋白具有阻止某些細(xì)菌附著在宿主細(xì)胞上的能力，粘附抑制的機(jī)制尚不清楚，但有研究認(rèn)為，乳鐵蛋白的寡甘露聚糖結(jié)合細(xì)菌粘附素，阻止它們與宿主細(xì)胞受體的相互作用。

2.4 防止細(xì)菌生物膜形成：

生物膜形成是銅綠假單胞菌的一種群聚組織粘附方法，在囊性纖維化患者中得到了充分的研究。通過(guò)生物膜的形成，細(xì)菌對(duì)宿主細(xì)胞的防御機(jī)制和抗生素的治療產(chǎn)生高度耐藥性，而一些細(xì)菌菌株需要高水平的鐵來(lái)形成生物膜，推測(cè)乳鐵蛋白通過(guò)鐵螯合來(lái)有效抑制生物膜的形成。

總體而言，乳鐵蛋白是人體內(nèi)具有抗多種微生物活性的重要物質(zhì)，是構(gòu)成人體體液免疫的關(guān)鍵組成部分，同時(shí)也可以作為生物制劑生產(chǎn)中的生物防腐劑，醫(yī)美藥品中抑菌、抗菌成分的重要原料，具有很高的經(jīng)濟(jì)價(jià)值。目前市面上的乳鐵蛋白主要從牛奶中提取，禾元生物依托自己的專利技術(shù)平臺(tái)—— 水稻胚乳細(xì)胞生物反應(yīng)器高效重組蛋白質(zhì)表達(dá)平臺(tái)(Oryz^HiExp)和重組蛋白純化技術(shù)平臺(tái)(Oryz^Pur)開(kāi)發(fā)了植物源重組人乳鐵蛋白，具有良好的生物活性。植物源重組乳鐵蛋白杜絕了天然乳鐵蛋白中動(dòng)物源、人源雜質(zhì)的風(fēng)險(xiǎn)，也比微生物源重組蛋白擁有更優(yōu)秀的折疊狀態(tài)，結(jié)構(gòu)功能與生物活性，為乳鐵蛋白市場(chǎng)提供了更安全更高質(zhì)的選擇。

參考文獻(xiàn)

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