You are provided with a publication (Kim, Dong Chung and Jin Jung, J.Microbiolog

Question

You are provided with a publication (Kim, Dong Chung and Jin Jung, J.Microbiology.Biotechnology, 2002) describing the purification of human Alpha-2a interferon, also known as hIFN?-2a. The test questions will require you to refer to text/figures in the journal article as well as the primary sequence characteristics. The primary sequence for the mature form of hIFN-2? is given as:

                    10                  20                      30                    40                     50

MALTFALLVA LLVLSCKSSC SVGCDLPQTH SLGSRRTLML LAQMRKISLF

                       60                    70                    80                    90                     100

SCLKDRHDFG FPQEEFGNQF QKAETIPVLH EMIQQIFNLF STKDSSAAWD

                 110                  120                    130               140                    150

ETLLDKFYTE LYQQLNDLEA CVIQGVGVTE TPLMKEDSIL AVRKYFQRIT

                 160                    170                180      

LYLKEKKYSP CAWEVVRAEI MRSFSLSTNL   QESLRSKE

The amino acid composition of the above sequence is as follows:

Ala (A) 8 4.8% Arg (R) 9 5.5% Asn (N) 4 2.4% Asp (D) 8 4.8% Cys (C) 4 2.4% Gln (Q) 12 7.3% Glu (E) 14 8.5% Gly (G) 5 3.0% His (H) 3 1.8% Ile (I) 8 4.8% Leu (L) 21 12.7% Lys (K) 11 6.7% Met (M) 5 3.0% Phe (F) 10 6.1% Pro (P) 5 3.0% Ser (S) 14 8.5% Thr (T) 10 6.1% Trp (W) 2 1.2% Tyr (Y) 5 3.0% Val (V) 7 4.2% Pyl (O) 0 0.0% Sec (U) 0 0.0

The first 23 residues of the primary sequence derived from the gene sequence (i.e., N-terminal to that shown in the preceding graphic) comprise a signal peptide.

i. What predominant chemical property would allow this sequence segment to be recognized as a signal sequence?

ii. What is the cellular event by which this sequence segment is lost to create the mature form of the protein?

iii. This paper describes the purification of recombinant protein prepared using E.coli cells.

What would be a likely compositional difference between this material and IFN?-2a as it occurs in human cells?

Reference material for this question is :  

J. Microbiol. Biotechnol. (2002), 12(6), 916–920

Purification of Recombinant Human Alpha-2a Interferon Without Using Monoclonal Antibodies

KIM, DONG CHUNG, AND JIN JUNG

Explanation / Answer

i) As we can see, the signal peptide comprises mostly hydrophobic amino acids and uncharged amino acids. Thus the presence of hydrophobic amino acids and uncharged hydrophilic amino acids marks the signal peptide.

Hydrophobic amino acids: G A V L I F P W M

Uncharged polar amino acids: S T C N Q Y

ii) The signal peptide is cleaved by signal peptidase enzyme which recognise the signal peptide and cleaves it during or after the translocation of protein.

iii) Unlike the IFN-2a from E.coli, the humnan IFN-2a will contain post transcriptional modification such as splicing and post translational modification such as phosphorylation and acetylation.

Related Questions

Navigate

• Browse (All)
• Browse Y
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.