Common Mechanisms for Regulating Pr

Common Mechanisms for Regulating
Protein Function
■ In allostery, the binding of one ligand molecule (a substrate, activator, or inhibitor) induces a conformational change, or allosteric transition, that alters a protein’s activity or affinity for other ligands.
■ In multimeric proteins, such as hemoglobin, that bind
multiple ligand molecules, the binding of one ligand molecule may modulate the binding affinity for subsequent ligand molecules. Enzymes that cooperatively bind substrates exhibit sigmoidal kinetics similar to the oxygen-binding
curve of hemoglobin (see Figure 3-26).
■ Several allosteric mechanisms act as switches, turning protein activity on and off in a reversible fashion.
■ The binding of allosteric ligand molecules may lead to the conversion of a protein from one conformationalactivity state into another or to the release of active subunits (see Figure 3-27).
■ Two classes of intracellular switch proteins regulate a
variety of cellular processes: (1) calmodulin and related Ca2-binding proteins in the EF hand family and (2) members of the GTPase superfamily (e.g., Ras and G
), which cycle between active GTP-bound and inactive GDP-bound forms (see Figure 3-29).
■ The phosphorylation and dephosphorylation of amino acid side chains by protein kinases and phosphatases provide reversible on/off regulation of numerous proteins.
■ Nonallosteric mechanisms for regulating protein activity include proteolytic cleavage, which irreversibly converts inactive zymogens into active enzymes, compartmentation of proteins, and signal-induced modulation of protein synthesis and degradation.

Hasil (Bahasa Indonesia) 2:

Umum Mekanisme untuk Mengatur
Protein Fungsi
■ Dalam allostery, pengikatan satu molekul ligan (substrat, aktivator, atau inhibitor) menginduksi perubahan konformasi, atau transisi alosterik, yang mengubah aktivitas protein atau afinitas untuk ligan lainnya.
■ Dalam protein multimerik, seperti hemoglobin, yang mengikat
beberapa molekul ligan, pengikatan satu molekul ligan dapat memodulasi afinitas mengikat molekul ligan berikutnya. Enzim yang kooperatif mengikat substrat menunjukkan kinetika sigmoidal mirip dengan oksigen mengikat
kurva hemoglobin (lihat Gambar 3-26).
■ Beberapa mekanisme alosterik bertindak sebagai switch, mengubah aktivitas protein dan mematikan secara reversibel.
■ Pengikatan ligan alosterik molekul dapat menyebabkan konversi protein dari satu negara ke conformationalactivity lain atau pelepasan subunit aktif (lihat Gambar 3-27).
■ Dua kelas protein saklar intraseluler mengatur sebuah
berbagai proses seluler: (1) kalmodulin dan terkait Ca2? -binding protein dalam keluarga EF tangan dan (2) anggota superfamili GTPase (misalnya, Ras dan G?), yang siklus antara aktif GTP-terikat dan tidak aktif PDB-terikat bentuk (lihat Gambar 3-29).
■ fosforilasi dan defosforilasi rantai samping asam amino oleh protein kinase dan fosfatase memberikan reversibel on / off regulasi banyak protein.
■ mekanisme Nonallosteric untuk mengatur aktivitas protein termasuk pembelahan proteolitik, yang ireversibel mengubah zymogens aktif menjadi enzim aktif, kompartemensi protein, dan sinyal modulasi -diinduksi sintesis protein dan degradasi.