Structure of Water ChannelsSince th

Structure of Water Channels

Since the initial discovery that a protein acts as a water channel in mammalian red blood cell membranes, additional water channels have been discovered in other tissues, with currently 10 (or 11) known mammalian water channels. CHIP28 [also known as aquaporin-1 (AQP1)] is now identified as a representative of this new class of transport proteins known as aquaporins. AQP1 has 269 amino acids forming two tandem repeats of three membrane-spanning -helices plus two short helical loops (B and E loops) within the lipid bilayer (31). Figure 2 shows the “hourglass” model of AQP1. The carboxy and amino termini are both cytoplasmic. The B loop connects helices 2 and 3 and the E loop connects helices 5 and 6. The connecting loops each contain an Asn-Pro-Ala (NPA) motif that appears to be the site of the channel for water. Sui et al. (26) conducted definitive analysis of AQP1 by X-ray crystallography down to a resolution of 2.2 Å and in so doing clarified the selectivity of the pore region for water molecules. The short helical B and E loops are two membrane-inserted non-membrane- spanning helices capped by Asn residues. The centrally located channel adjacent to these loops has a constriction of
2.8 Å (water molecules have a radius of 2.8 Å). Thus the pore itself consists of an extracellular and a cytoplasmic vestibule connected by an extended narrow pore with a long hydrophobic core and a minimal number of solute-binding sites. Residues in the region of the constriction (particularly histidine-182, which is conserved in the aquaporin family) are critical for the selectivity of the channel for water molecules. The hydrophilic face of the pore provides the chemical groups for displacing waters of hydration to establish a pathway for coordinating the
transport of water molecules. It appears that the formation of hydrogen bonds between water molecules and the pore residues causes the specificity of the channel for water. Water molecules permeate the channel single file and break hydrogen bonds with each other to form one and then the other hydrogen bonds with residues of the B and E loops within the channel

Hasil (Bahasa Indonesia) 1:

Struktur saluran airSince the initial discovery that a protein acts as a water channel in mammalian red blood cell membranes, additional water channels have been discovered in other tissues, with currently 10 (or 11) known mammalian water channels. CHIP28 [also known as aquaporin-1 (AQP1)] is now identified as a representative of this new class of transport proteins known as aquaporins. AQP1 has 269 amino acids forming two tandem repeats of three membrane-spanning -helices plus two short helical loops (B and E loops) within the lipid bilayer (31). Figure 2 shows the “hourglass” model of AQP1. The carboxy and amino termini are both cytoplasmic. The B loop connects helices 2 and 3 and the E loop connects helices 5 and 6. The connecting loops each contain an Asn-Pro-Ala (NPA) motif that appears to be the site of the channel for water. Sui et al. (26) conducted definitive analysis of AQP1 by X-ray crystallography down to a resolution of 2.2 Å and in so doing clarified the selectivity of the pore region for water molecules. The short helical B and E loops are two membrane-inserted non-membrane- spanning helices capped by Asn residues. The centrally located channel adjacent to these loops has a constriction of
2.8 Å (water molecules have a radius of 2.8 Å). Thus the pore itself consists of an extracellular and a cytoplasmic vestibule connected by an extended narrow pore with a long hydrophobic core and a minimal number of solute-binding sites. Residues in the region of the constriction (particularly histidine-182, which is conserved in the aquaporin family) are critical for the selectivity of the channel for water molecules. The hydrophilic face of the pore provides the chemical groups for displacing waters of hydration to establish a pathway for coordinating thetransportasi molekul air. Tampaknya bahwa pembentukan ikatan hidrogen antara molekul air dan residu pori-pori menyebabkan kekhasan saluran air. Molekul air meresap saluran file tunggal dan mematahkan ikatan hidrogen dengan satu sama lain untuk membentuk satu dan kemudian ikatan hidrogen lain dengan residu loop B dan E dalam saluran

Hasil (Bahasa Indonesia) 2:

Struktur Saluran Air

Sejak penemuan awal yang protein bertindak sebagai saluran air dalam membran sel darah merah mamalia, saluran air tambahan telah ditemukan di jaringan lain, dengan saat ini 10 (atau 11) dikenal saluran air mamalia. CHIP28 [juga dikenal sebagai aquaporin-1 (AQP1)] sekarang diidentifikasi sebagai wakil dari kelas baru dari protein transport yang dikenal sebagai aquaporins. AQP1 memiliki 269 asam amino membentuk dua mengulangi tandem dari tiga -helices membran-spanning ditambah dua loop heliks pendek (B dan E loop) dalam bilayer lipid (31). Gambar 2 menunjukkan "jam pasir" model AQP1. The karboksi dan amino termini keduanya sitoplasma. B lingkaran menghubungkan heliks 2 dan 3 dan loop E menghubungkan heliks 5 dan 6. loop menghubungkan masing-masing berisi sebuah Asn-Pro-Ala (NPA) motif yang tampaknya menjadi tempat saluran air. Sui et al. (26) melakukan analisis definitif AQP1 oleh X-ray kristalografi ke resolusi 2,2 Å dan dengan demikian menjelaskan selektivitas wilayah pori untuk molekul air. Pendek heliks B dan E loop dua heliks mencakup non-pada membran-membran dimasukkan dibatasi oleh residu Asn. Saluran ini terletak berdekatan dengan loop ini memiliki penyempitan? 2,8 Å (molekul air memiliki radius 2,8 Å). Sehingga pori itu sendiri terdiri dari ekstraseluler dan ruang depan sitoplasma terhubung oleh pori sempit diperpanjang dengan hidrofobik inti panjang dan jumlah minimal situs zat terlarut-mengikat. Residu di wilayah penyempitan (terutama histidin-182, yang dilestarikan dalam keluarga aquaporin) sangat penting untuk selektivitas saluran untuk molekul air. Wajah hidrofilik dari pori-pori memberikan kelompok kimia untuk menggusur perairan hidrasi untuk membangun jalur untuk mengkoordinasikan
transportasi molekul air. Tampak bahwa pembentukan ikatan hidrogen antara molekul air dan residu pori menyebabkan kekhususan saluran air. Molekul air menembus saluran file tunggal dan memecah ikatan hidrogen dengan satu sama lain untuk membentuk satu dan kemudian ikatan hidrogen lain dengan residu dari B dan E loop dalam saluran