ミトコンドリアの外膜の前タンパク質転位チャネル
K P Künkele1, S Heins, M Dembowski
1Institut für Physiologische Chemie, Physikalische Biochemie, und Zellbiologie der Universität München, Germany.
Cell
|July 11, 1998
まとめ
研究者は,ミトコンドリア外膜トランスロカゼ (TOM複合体) を浄化し,その中にカチオン選択チャネルが含まれていることを発見しました. このチャネルは,ミトコンドリア外膜にタンパク質の転位を容易にする.
科学分野:
- ミトコンドリア生物学 ミトコンドリア生物学
- 蛋白質の転位によるタンパク質転位です.
- 膜バイオフィジックス
背景:
- ミトコンドリアの外膜は,ミトコンドリアへのタンパク質の輸入を制御します.
- 外膜 (TOM) 複合体のプロテイン前トランスロカゼは,このプロセスにおいて極めて重要です.
- TOM複合体の構造と機能を理解することは,ミトコンドリア生物発生の鍵です.
研究 の 目的:
- Neurospora crassa.からTOM複合体を浄化し特徴づけること.
- TOM複合体の構造的,機能的特性を解明する.
- TOM複合体内のタンパク質伝導チャネルを特定する.
主な方法:
- ニューロスポラ・クラッサからTOM複合体の浄化.
- TOM複合体をリポソームに再構成する.
- チャンネル活性とタンパク質転位の分析.
- 電子顕微鏡と構造的決定のための画像分析.
主要な成果:
- 浄化されたTOM複合体は,カチオン選択性,高伝導性チャネル活性を示しています.
- 再構成されたTOM複合体は,脂質二層にわたってタンパク質の統合と転位を媒介する.
- 電子顕微鏡では,直径約138 ÅのTOM複合粒子を検出しました.
- 構造分析により,直径約20 Åの2〜3個の毛孔開口が確認されました.
結論:
- 浄化されたTOM複合体は,タンパク質伝導チャネルとして機能する.
- 構造データは,ミトコンドリアタンパク質の輸入のメカニズムについての洞察を提供します.
- この研究は,ミトコンドリアタンパク質トランスロカゼの機能的および構造的基礎を特徴づけています.
関連する概念動画
Mitochondrial Protein Sorting
Mitochondria are double-membrane organelles of the eukaryotes involved in cellular metabolism, signaling, ATP synthesis, and programmed cell death. Each of these processes requires specific proteins and enzymes that must be correctly sorted to the right mitochondrial subcompartment for the proper functioning of the organelle.
Most of these mitochondrial proteins are encoded by the nucleus and imported to the mitochondria as unfolded or loosely folded precursors. Mitochondrial precursors...
Most of these mitochondrial proteins are encoded by the nucleus and imported to the mitochondria as unfolded or loosely folded precursors. Mitochondrial precursors...
Mitochondrial Precursor Proteins
Mitochondrial precursors are partially unfolded or loosely folded polypeptide chains. Newly synthesized precursors are inhibited from spontaneously folding into their native conformation by the cytosolic chaperones, heat shock proteins 70 (Hsp70), and mitochondrial import stimulation factors (MSFs). Precursors bound to MSFs are guided to the TOM70-TOM37 receptors, while precursors bound to Hsp70 chaperones are targetted to TOM20-TOM22 receptor complexes.
Most of the mitochondrial precursors...
Most of the mitochondrial precursors...
Translocation of Proteins into the Mitochondria
Mitochondrial precursors are translocated to the internal subcompartments via independent mechanisms involving distinct protein machineries called translocases.
Sorting of outer membrane proteins:
Mitochondrial outer membrane proteins are of two types: the transmembrane, beta-barrel porins, and the membrane-anchored, alpha-helical proteins. Beta-barrel porin precursors are translocated by the TOM complex and inserted into the outer mitochondrial membrane by the SAM complex. In contrast,...
Sorting of outer membrane proteins:
Mitochondrial outer membrane proteins are of two types: the transmembrane, beta-barrel porins, and the membrane-anchored, alpha-helical proteins. Beta-barrel porin precursors are translocated by the TOM complex and inserted into the outer mitochondrial membrane by the SAM complex. In contrast,...
Energy to Drive Translocation
Mitochondrial protein import is powered by two distinct energy sources: ATP hydrolysis and electrochemical potential across the inner membrane. Newly synthesized precursors are bound by cytosolic chaperones of the Hsp70 family, which guide them to the import receptors on the mitochondrial surface. Utilizing the energy of ATP hydrolysis, Hsp70 chaperones transfer these precursors to the TOM receptors on the mitochondrial outer membrane.
Generally, polypeptides are unfolded by two distinct...
Generally, polypeptides are unfolded by two distinct...
Porin Insertion in the Outer Mitochondrial Membrane
Porins are beta-barrel proteins translocated to the mitochondrial outer membrane through the TOM complex into the intermembrane space. Porin precursors bind TIM chaperones within the intermembrane space and are guided to the Sorting and Assembly Machinery complex or SAM complex on the outer mitochondrial membrane.
Three models describe the assembly of porins by the SAM complex and their insertion into the outer membrane. Model 1 suggests that porins are assembled outside the SAM channel as the...
Three models describe the assembly of porins by the SAM complex and their insertion into the outer membrane. Model 1 suggests that porins are assembled outside the SAM channel as the...
Protein Transport into the Inner Mitochondrial Membrane
Nuclear encoded mitochondrial precursors are imported to the inner membrane in a multistep process involving two separate translocons, TIM22 and TIM23. TIM23 is a cation-selective pore that remains closed by the N terminal segment of the protein. Negative charges on the TIM23 act as a receptor for the incoming precursor, pulling the positively charged matrix-targeting sequence for peptide insertion and translocation.
Transport of mitochondrial precursors across the TIM23 channel is driven by...
Transport of mitochondrial precursors across the TIM23 channel is driven by...


