WBR0848

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Serge Korjian)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biochemistry
Sub Category	SubCategory::General Principles
Prompt	[[Prompt::A 78-year-old man presents to the emergency department for pleuritic chest pain. Following a complete work-up, the diagnosis of viral pneumonia due to influenza is made. The physician explains that in addition to viral factors, host factors are also needed for an infection to occur. Which of the following host factors is required for the influenza virus to enter the cell?]]
Answer A	AnswerA::Hemagglutinin
Answer A Explanation	AnswerAExp::Hemagglutinin is a viral factor that promotes viral entry.
Answer B	AnswerB::Neuraminidase
Answer B Explanation	AnswerBExp::Neuraminidase is a viral factor that promotes release of viral progeny.
Answer C	AnswerC::Clathrin
Answer C Explanation	AnswerCExp::Clathrin is a protein that mediates the uptake of compounds by endocytosis.
Answer D	AnswerD::Kinesin
Answer D Explanation	AnswerDExp::Kinesin is a protein that allows the transport of membrane-bound organelles from the (-) pole of the microtubule to its (+) pole.
Answer E	AnswerE::Hematin
Answer E Explanation	AnswerEExp::Hematin (factor X) is produced by H. influenza, gram negative bacteria, not by influenza virus.
Right Answer	RightAnswer::C
Explanation	[[Explanation::Influenza virus is an enveloped virus that contains 3 major proteins: Hemagglutinin (HA), neuromanidase (NA), and M2 that are present on its lipid bilayer membrane. Protein matrix under the lipid bilayer membrane is made of M1 protein. Viral entry into the cells starts with viral internalization by receptor-mediated endocytosis. Viruses are then trafficked along the endocytic pathway to endosomes. Viral factors, such as HA and NA are needed for the attachment of the virus to the cell and subsequent entry. At the same time, host factors, such as clathrin, are needed for the endocytosis. Clathrin is a protein that is important for the formation of vesicles needed for endocytosis. Clathrin is a large protein with light and heavy chains that forms "clathrin-coated vesicles" (CCV). It is able to transport proteins inside the cells between organelles to their target destination. Educational Objective: Clathrin-mediated endocytosis is required by some viruses, such as influenza virus, for cell entry. References: Lakadamyali M, Rust M, Zhuang X. Endocytosis of influenza virus. Microbes Infect. 2004; 6(10):929-936.]]
Approved	Approved::Yes
Keyword	WBRKeyword::Clathrin, WBRKeyword::Receptor mediated endocytosis, WBRKeyword::Endocytosis, WBRKeyword::Influenza, WBRKeyword::Influenza virus, WBRKeyword::Hemagglutinin
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